{%= image_tag "/images/richard_stallman.jpg", :alt => "[Richard Stallman]" %}UNIX is an extremely popular platform for deploying server software partly because of its security and stability, but also because it has a rich set of command line and scripting tools. Programmers use these tools for manipulating the file system, processing log files, and generally automating as much as possible. If you want to be a serious server developer, you will need to have a certain facility with a number of UNIX tools; about 15. You will start to see similarities among them, particularly regular expressions, and soon you will feel very comfortable. Combining the simple commands, you can build very powerful tools very quickly—much faster than you could build the equivalent functionality in C or Java, for example. ## Wszystko jest strumieniem The first thing you need to know is that UNIX is based upon the idea of a *stream*. Everything is a *stream*, or appears to be. Device drivers look like streams, terminals look like streams, processes communicate via streams, etc… The input and output of a program are streams that you can redirect into a device, a file, or another program. Here is an example device, the null device, that lets you throw output away. For example, you might want to run a program but ignore the output. :::shell-unix-generic ls > /dev/null # ignore output of ls where "`# ignore output of ls`" is a comment. Most of the commands covered in this lecture process `stdin` and send results to `stdout`. In this manner, you can incrementally process a data stream by hooking the output of one tool to the input of another via a *pipe*. For example, the following piped sequence prints the number of files in the current directory modified in August. :::shell-unix-generic ls -l | grep ' 10-' | wc -l Imagine how long it would take you to write the equivalent C or Java program. You can become an extremely productive UNIX programmer if you learn to combine the simple command-line tools. Even when programming on a PC, I use MKS's UNIX shell and command library to make it look like a UNIX box. Worth the cash. ## Uzyskiwanie pomocy If you need to know about a command, ask for the "man" page. For example, to find out about the `ls` command, type :::shell-unix-generic man ls LS(1) User Commands LS(1) NAME ls - list directory contents SYNOPSIS ls [OPTION]... [FILE]... DESCRIPTION List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor --sort. ... You will get a summary of the command and any arguments. If you cannot remember the command's name, try using `apropos` which finds commands and library routines related to that word. For example, to find out how to do checksums, type apropos '\bgit\b' gitrepository [] (5) - layout - Git Repository Layout gittutorial [] (7) - A tutorial introduction to git gitworkflows [] (7) - An overview of recommended workflows with git ## Special Directories and files A shortcut for my home directory, `/home/pracinf/wbzyl`, is `~wbzyl`. When you are using the shell, there is the notion of current directory. The dot '`.`' character is a shorthand for the current directory and '`..`' is a shorthand for the directory above the current. So to access file `test` in the current directory, `./test` is the same as plain `test`. If `test` is a directory above, use `../test`. `/` is the root directory; there is no drive specification in UNIX. The `.bash_profile` file is very important as it is how your shell session is initialized including your ever-important `PATH` environment variable. My `bash` shell initialization file is `~wbzyl/.bash_profile` and has set up code like the following: :::shell-unix-generic PATH=$PATH:$HOME/bin export PATH The `export` means that the assignment to `PATH` is visible to all child processes (that is, visible to all programs you run from the shell). ## Podstawowe polecenia ### cd Changing a directory is done with `cd` dir where dir can be "." or ".." to move to current directory (do nothing) or go up a directory. ### ls Display files in a directory with `ls`. The `-l` option is used to display details of the files: :::shell-unix-generic total 1234 drwxr-xr-x 5 wbzyl pracinf 4096 08-04 00:08 public_git drwx--x--x 2 wbzyl pracinf 4096 08-02 20:20 public_html drwxr-xr-x 7 wbzyl pracinf 4096 08-02 10:10 rpm drwx--x--x 2 wbzyl pracinf 4096 08-02 10:00 tmp ... "pracinfo" is wbzyl's group. If you want to see hidden files (those starting with "."), use `-a`. Combinations are possible: use `ls -la` to see details of all files including hidden ones. ### wyświetlanie zawartości plików There are 4 useful ways to display the contents or portions of a file. The first is the very commonly used command `cat`. For example, to display my email box, type: :::shell-unix-generic cat /var/mail/wbzyl If a file is really big, you will probably want to use `more`, which spits the file out in screen-size chunks. :::shell-unix-generic more /var/mail/wbzyl If you only want to see the first few lines of a file or the last few lines use `head` and `tail`. :::shell-unix-generic head /var//mail/wbzyl tail /var/mail/wbzyl You can specify a number as an argument to get a specific number of lines: :::shell-unix-generic head -30 /var/mail/wbzyl The most useful incantation of `tail` prints the last few lines of a file and then waits, printing new lines as they are appended to the file. This is great for watching a log file: :::shell-unix-generic tail -f /var/mail/wbzyl If you need to know how many characters, words, or lines are in a file, use `wc`: :::shell-unix-generic wc /var/mail/mail 100 1000 40000 /var/mail/wbzyl Where the numbers are, in order, lines, words, then characters. For clarity, you can use `wc -l` to print just the number of lines. ### pushd, popd Instead of `cd` you can use `pushd` to save the current dir and then automatically `cd` to the specified directory. For example, :::shell-unix-generic pwd /home/pracinf/wbzyl pushd /tmp /tmp ~ pwd /tmp popd ~ pwd /home/pracinf/wbzyl ### top (htop) To watch a dynamic display of the processes on your box in action, use `top` or `htop`. ### ps To print out (wide display) all processes running on a box, use :::shell-unix-generic ps auxww # double w ### chmod To change the privileges of a file or directory, use `chmod`. The privileges are 3 digit octal words with 3 bits per digit: rwxrwxrwx where the first digit is for the file owner, the 2nd for the group, and 3rd for anybody. 644 is a common word value file which means 110100100 or :::shell-unix-generic rw-r--r-- When you do `ls -l` you will see these bits. 755 is a common word value for directories: :::shell-unix-generic rwxr-xr-x where directories need to be executable for `cd` to be able to enter that dir. 755 is a shorthand for the more readable argument u=rwx,go=rx u is user, g is group, o is other. Use `chmod -R` for recursively applying to all the dirs below the argument as well. ## Searching streams One of the most useful tools available on UNIX and the one you may use the most is `grep`. This tool matches regular expressions (which includes simple words) and prints matching lines to `stdout`. The simplest incantation looks for a particular character sequence in a set of files. Here is an example that looks for lines begining with 'Return-Path:' in the IMAP mails in the current directory. :::shell-unix-generic grep '^Return-Path:' *,{S,RS,ST,FRST} You may find the dot '.' regular expression useful. It matches any single character but is typically combined with the star, which matches zero or more of the preceding item. Be careful to enclose the expression in single quotes so the command-line expansion doesn't modify the argument. The following example, looks for references to any a forum page in a server log file: :::shell-unix-generic sudo egrep '/forum/.*' /var/log/httpd/access_log or equivalently: :::shell-unix-generic sudo cat /var/log/access_log | grep '/forum/.*' The second form is useful when you want to process a collection of files as a single stream as in: :::shell-unix-generic sudo cat /var/log/httpd/*_log | grep '/forum/.*' If you need to look for a string at the beginning of a line, use caret '^': :::shell-unix-generic grep '^153.19.7.230' /var/log/httpd/access_log This finds all lines in all access logs that begin with IP address 153.19.7.230. If you would like to invert the pattern matching to find lines that do not match a pattern, use `-v`. Here is an example that finds references to non image `GET`s in a log file: :::shell-unix-generic sudo cat /var/log/access_log | grep -v '/images' Now imagine that you have an http log file and you would like to filter out page requests made by nonhuman spiders. If you have a file called `spider.ips`, you can find all nonspider page views via: :::shell-unix-generic cat /var/log/httpd/access_log | grep -v -f /tmp/spider.ips Finally, to ignore the case of the input stream, use `-i`. ## Przekształcanie strumieni tekstu Morphing a text stream is a fundamental UNIX operation. ### tr For manipulating whitespace, you will find `tr` very useful. If you have columns of data separated by spaces and you would like the columns to collapse so there is a single column of data, tell `tr` to replace space with newline `tr ' ' '\n'`. Consider input file `falski.txt`: :::shell-unix-generic ala ma kota ola ma psa To get all those names in a column, use :::shell-unix-generic cat falski.txt | tr ' ' '\n' If you would like to collapse all sequences of spaces into one single space, use `tr -s ' '`. To convert a PC file to UNIX, you have to get rid of the '\r' characters. Use `tr -d '\r'`. ### sed If dropping or translating single characters is not enough, you can use `sed` (stream editor) to replace or delete text chunks matched by regular expressions. For example, to replace all references to text *TT* by *kbd* in the file *ug.rdiscount*, use :::shell-unix-generic cat /ug.rdiscount | sed -r 's/TT/kbd/g' If there are multiple references to *TT* on a single line, use the `g` suffix to indicate "global" on that line otherwise only the first occurrence will be removed: :::shell-unix-generic ... | sed -r 's/TT/kbd/g' If you would like to replace references to *view.html* with *index.html*, use :::shell-unix-generic ... | sed 's/view.html/index.html/' If you want any `.pas` file converted to `.p`, you must match the file name with a regular expression and refer to it via `\1`: :::shell-unix-generic ... | sed 's/\(.*\).pas/\1.p/' The `\(...\)` grouping collects text that you can refer to with `\1`. If you want to kill everything from the ',' character to end of line, use the end-of-line marker `$`: :::shell-unix-generic ... | sed 's/,.*$//' # kill from comma to end of line ## Tarballs Note: *The name comes from a similar word, **hairball** (stuff that cats throw up), I'm pretty sure.* To collect a bunch of files and directories together, use `tar`. To tar up and gzip your entire home directory and put the gzipped tarball into `/tmp`, do this :::shell-unix-generic cd ~/.. # go one dir above dir you want to tar.gz; why? tar zcvf /tmp/wbzyl.backup.tar.gz wbzyl By convention, use `.tar.gz` as the extension. To ungzip and untar this file use :::shell-unix-generic cd ~/tmp tar zxvf /tmp/wbzyl.backup.tar.gz `tar` untars things in the **current** directory! After running the untar, you will find a new directory, `~/tmp/wbzyl`, that is a copy of your home directory. Note that the way you tar things up dictates the directory structure when untarred. The fact that I mentioned `wbzyl` in the tar creation means that I'll have that dir when untarred. In contrast, the following will also make a copy of my home directory, but without having a `parrt` root dir: :::shell-unix-generic cd ~wbzyl tar cvf /tmp/wbzyl.backup.tar * It is a good idea to tar things up with a root directory so that when you untar you don't generate a million files in the current directly. To see what's in a tarball, use :::shell-unix-generic tar ztvf /tmp/wbzyl.backup.tar.gz If you have a big file to compress, use `gzip`: :::shell-unix-generic gzip bigfile After execution, your file will have been renamed `bigfile.gz`. To uncompress, use :::shell-unix-generic gzip -d bigfile.gz To display a text file that is currently `gzip`'d, use `zcat`: :::shell-unix-generic zcat bigfile.gz ## Kopiowanie plików między komputerami ### rsync When you need to have a directory on one machine mirrored on another machine, use `rsync`. It compares all the files in a directory subtree and copies over any that have changed to the mirrored directory on the other machine. For example, here is how you could "pull" all css screencasts files from `renia.local` to the box from which you execute the `rsync` command: :::shell-unix-generic hostname -f wlodek.local rsync -raz -e ssh -v wlodek@renia.local:screencasts/css-tricks.com \ ~/backup/ ls ~/backup/css-tricks.com/ VideoCast-57-css3.m4v ... `rsync` will delete or truncate files to ensure the files stay the same. This is bad if you erase a file by mistake--it will wipe out your backup file. Change the options above to `-rabz` to tell `rsync` to make a copy of any existing file before it overwrites it. Or change a filename of any existing file: :::shell-unix-generic rsync -rabz -e ssh -v --suffix .rsync_`date '+%Y%m%d'` \ wlodek@renia.local:screencasts/css-tricks.com ~/backup/ where ``date '+%Y%m%d'`` (in reverse single quotes) means "execute this `date` command". To exclude certain patterns from the sync, use `--exclude`: :::shell-unix-generic rsync -rabz --exclude=tmp/ --suffix .rsync_`date '+%Y%m%d'` \ -e ssh -v wbzyl@renia.local:screencasts/css-tricks.com' ~/backup/ ### scp To copy a file or directory manually, use `scp`: :::shell-unix-generic scp lecture.html wbzyl@sigma.ug.edu.pl:public_html/ Just like `cp`, use `-r` to copy a directory recursively. ## Pozostałe programy ### find Most GUIs for Linux or PCs have a search facility, but from the command-line you can use `find`. To find all files with suffix `.c` starting in directory `~/projects`, use: :::shell-unix-generic find ~/projects -name '.c' The default "action" is to `-print`. You can specify a globbing pattern to match. For example, to look under your home directory for any xml files, use: :::shell-unix-generic find ~ -name '*.xml' -print Note the use of the single quotes to prevent command-line expansion--you want the '*' to go to the `find` command. You can execute a command for every file or directory found that matches a name. For example, do delete all xml files, do this: :::shell-unix-generic find ~ -name '*.xml' -exec rm {} \; where "{}" stands for "current file that matches". The end of the command must be terminated with ';' but because of the command-line expansion, you'll need to escape the ';'. You can also specify time information in your query. Here is a shell script that uses `find` to delete all files older than 14 days. :::shell-unix-generic #!/bin/sh BACKUP_DIR=$HOME/backup # number of days to keep backups AGE=14 # days AGE_MINS=$[ $AGE * 60 * 24 ] # delete dirs/files find $BACKUP_DIR/* -cmin +$AGE_MINS -type d -exec rm -rf {} \; ### fuser If you want to know who is using a port such as HTTP (80), use `fuser`. You must be root to use this: :::shell-unix-generic sudo /sbin/fuser -n tcp 80 80/tcp: 1812 1884 1892 1898 The output indicates the list of processes associated with that port. ### whereis Sometimes you want to use a command but it's not in your `PATH` and you can't remember where it is. Use `whereis` to look in standard unix locations for the command. :::shell-unix-generic whereis fuser fuser: /sbin/fuser /usr/man/man1/fuser.1 /usr/man/man1/fuser.1.gz whereis ls ls: /bin/ls /usr/man/man1/ls.1 /usr/man/man1/ls.1.gz `whereis` also shows `man` pages. ### which, type Sometimes you might be executing the wrong version of a command and you want to know which version of the command your `PATH` indicates should be run. Use `which` to ask: :::shell-unix-generic which ls alias ls='ls --color=tty' /bin/ls type ls ls is aliased to `ls --color=auto' If nothing is found in your path, you'll see: :::shell-unix-generic which fuser /usr/bin/which: no fuser in (/usr/local/bin:/usr/X11R6/bin) ### kill, pkill To send a signal to a process, use `kill`. Typically you'll want to just say `kill pid` where `pid` can be found from `ps` or `top` (see below). Use `kill -9 pid` when you can't get the process to die; this means kill it with "extreme prejudice". ### tracepath, traceroute If you are having trouble getting to a site, use `traceroute` to watch the sequence of hops used to get to a site: :::shell-unix-generic /usr/sbin/tracepath sigma.ug.edu.pl 1: wlodek.local 0.391ms pmtu 1500 ... 5: do.gda-ar3.z.gda-r2.tpnet.pl (213.25.12.95) 10.854ms asymm 6 6: TP-tp-edu-gw.task.gda.pl (153.19.0.2) 42.373ms asymm 13 7: tp-jra10ge.task.gda.pl (153.19.252.33) 34.889ms asymm 12 8: area1-ug1-swr.task.gda.pl (153.19.254.228) 34.365ms asymm 12 9: sigma.ug.edu.pl (153.19.7.230) 36.318ms reached Resume: pmtu 1500 hops 9 back 52 sudo /bin/traceroute sigma.ug.edu.pl traceroute to sigma.ug.edu.pl (153.19.7.230), 30 hops max, 60 byte packets 1 wlodek.local 1.708 ms 2.529 ms 3.330 ms ... 5 do.gda-ar3.z.gda-r2.tpnet.pl (213.25.12.95) 21.905 ms 22.052 ms 30.636 ms 6 TP-tp-edu-gw.task.gda.pl (153.19.0.2) 42.546 ms 33.290 ms 33.401 ms 7 tp-jra10ge.task.gda.pl (153.19.252.33) 38.472 ms 38.876 ms 39.371 ms 8 area1-ug1-swr.task.gda.pl (153.19.254.228) 41.536 ms 41.720 ms 41.916 ms 9 sigma.ug.edu.pl (153.19.7.230) 39.618 ms 39.921 ms 40.236 ms ### Jaki jest mój adres IP? :::shell-unix-generic /sbin/ifconfig or :::shell-unix-generic /sbin/ifconfig eth0 Under the `eth0` interface, you'll see the `inet addr`: :::shell-unix-generic eth0 Link encap:Ethernet HWaddr 00:0E:35:95:80:44 inet addr:192.188.100.1 Bcast:192.188.100.255 Mask:255.255.255.0 inet6 addr: fe00::40a:32ca:c950:1234/64 Scope:Link ## Użyteczne potoki: generowanie histogramu A histogram is set of count, value pairs indicating how often the value occurs. The basic operation will be to sort, then count how many values occur in a row and then reverse sort so that the value with the highest count is at the top of the report. :::shell-unix-generic ... | sort |uniq -c|sort -r -n Note that `sort` sorts on the whole line, but the first column is obviously significant just as the first letter in someone's last name significantly positions their name in a sorted list. `uniq -c` collapses all repeated sequences of values but prints the number of occurrences in front of the value. Recall the previous sorting: :::shell-unix-generic cut -d ' ' -f 7 access_log | egrep '^/sp/' | \ sort | \ uniq /sp/ /sp/exercises /sp/git /sp/images/alan_kay.jpg /sp/images/alan_perlis.jpg /sp/images/albert_einstein.jpg ... Now add `-c` to `uniq`: :::shell-unix-generic cut -d ' ' -f 7 access_log | egrep '^/sp/' | \ sort | \ uniq -c 22 /sp/ 6 /sp/exercises 2 /sp/git 1 /sp/images/alan_kay.jpg 2 /sp/images/alan_perlis.jpg 4 /sp/images/albert_einstein.jpg ... Now all you have to do is reverse sort the lines according to the first column numerically. :::shell-unix-generic cut -d ' ' -f 7 access_log | egrep '^/sp/' | \ sort | \ uniq -c | \ sort -r -n 51 /sp/stylesheets/uv.css 51 /sp/stylesheets/sp.css 51 /sp/stylesheets/screen.css 51 /sp/stylesheets/print.css 50 /sp/stylesheets/icons/external.png ...Richard M. Stallman, Linus Torvalds, and Donald E. Knuth engage in a discussion on whose impact on the computerized world was the greatest.
Stallman: "God told me I have programmed the best editor in the world!" Torvalds: "Well, God told *me* that I have programmed the best operating system in the world!" Knuth: "Wait, wait – I never said that."