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2011-03-12 - Confoo 2011 presentation
Slides are available from the commandlinefu presentation at Confoo 2011: http://presentations.codeinthehole.com/confoo2011/
2011-01-04 - Moderation now required for new commands
To try and put and end to the spamming, new commands require moderation before they will appear on the site.
2010-12-27 - Apologies for not banning the trolls sooner
Have been away from the interwebs over Christmas. Will be more vigilant henceforth.
2010-09-24 - OAuth and pagination problems fixed
Apologies for the delay in getting Twitter's OAuth supported. Annoying pagination gremlin also fixed.

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Commands using cat from sorted by
Terminal - Commands using cat - 431 results
cat file.txt | sendmail -F myname -f [email protected] [email protected]
while :; do cat file.txt | nc -l 80; done
cat x
cat /proc/PID/environ | tr '\0' '\n'
cat aaaaaa 2>&-
cat -n file.txt
cat file.csv | perl -pe 'if($. == 1) {@h = split(/;/); $i = 1 ; map { $_ = $i; $i++ } @h; print join(" ;", @h) , "\n"} ; s/(^|;);/$1 ;/g' | column -ts\; | less -S
echo $(cat /usr/share/dict/words |grep -v "'"|shuf -n4)
2011-08-31 12:48:14
User: d1v3rdown
Functions: cat echo grep
Tags: cat echo grep shuf

Fast and excludes words with apostrophes. For ubuntu, you can use wamerican or wbritish dictionaries, installable through aptitude.

cat /etc/passwd | column -nts:
mkdir replaced;for i in *; do cat "$i"| sed 's/foo/bar/' > "replaced/$i"; done
2011-08-30 08:28:26
User: rubo77
Functions: cat mkdir sed

if you want to replace "foo" with "bar" in all files in a folder, and put the resulting files into a new subfolder

cat dirtyfile.txt | awk '{gsub(/[[:punct:]]/,"")}1' | tr A-Z a-z | sed 's/[0-9]*//g' | sed -e 's/ //g' | strings | tr -cs '[:alpha:]' '\ ' | sed -e 's/ /\n/g' | tr A-Z a-z | sort -u > cleanfile.txt
2011-08-28 01:26:04
User: purehate
Functions: awk cat sed sort strings tr

Using large wordlists is cumbersome. Using password cracking programs with rules such as Hashcat or John the ripper is much more effective. In order to do this many times we need to "clean" a wordlist removing all numbers, special characters, spaces, whitespace and other garbage. This command will covert a entire wordlist to all lowercase with no garbage.

x=(*.001); cat "${x%.001}."* > "${x%.001}" #unsafe; does not check that all the parts are there, or that the file-sizes make sense!
2011-08-24 04:10:20
User: Jessehz
Functions: cat make

Join all sequentially named files in the directory.

Use this for files split by utilities like hjsplit and similar.

This command does not do/perform _any_ sanity checks before acting, except that it won't run unless there is a file that matches "*.001".

- The outfile should not already exist.

- There should be more than one file. (*.002 should exist as well as *.001)

- The file-count should match the number in the name of the last file in the series.

- None of the files should be empty.

- All files should be the same size, except for the last, which should usually be smaller, but never larger than the rest.

A safer altenative can be found here: http://pastebin.com/KSS0zU2F

cat /usr/share/dict/words | grep -P ^[a-z].* | grep -v "'s$" | grep -Pv ^.\{1,15\}$ | shuf -n4 | tr '\n' ' ' | sed 's/$/\n/'
2011-08-15 01:03:48
User: bugmenot
Functions: cat grep sed tr
Tags: tr xkcd shuf

The first grep rejects capitalised words since the dict has proper nouns in it that you mightn't want to use. The second grep rejects words with ending in apostrophe s, and the third forces the words to be at least 15 characters long.

cat input.txt | sed 's/\\\033[^a-zA-Z]*.//g'
cat subtitles.txt | perl -pe 's/} /}/g; s/{(\d+)}/=1=/; $f1=(24/25*$1); s/{(\d+)}/=2=/; $f2=(24/25*$1); $f1=~s/\..*//; $f2=~s/\..*//; s/=1=/{$f1}/; s/=2=/{$f2}/; ' > subtitles_newfps.txt
2011-07-30 15:34:43
User: ciekawy
Functions: cat perl

this command example converts to 25 fps subtitles that were originally created for 24 fps movie

find src/ -name "*.java" | while read f; do echo -n "$f "; cat "$f" | tr -dc '{}'; echo; done | awk '{ print length($2), $1 }' | sort -n
pdftk input1.pdf input2.pdf cat output output.pdf
MAC=$((date +'%Y%m%d%H%M%S%N'; cat /proc/interrupts) | md5sum | sed -r 's/(..)/\1:/g' | cut -d: -f 1-6)
2011-07-14 13:11:50
User: jazznjam
Functions: cat cut date md5sum sed

I liked vaporub's suggestion, here a little simplification of the sed command.

cat video.avi.001 video.avi.002 video.avi.003 >> video.avi
cat my.sandbox.cnf | awk -F "=" 'NF < 2 {print} sub("=", "=~placeholder~=") {print}' | awk -F "=~placeholder~=" 'NF < 2 {gsub("-", "_", $0); print} NF==2 {gsub("-", "_", $1); print $1 "=" $2}'
2011-07-06 09:35:55
User: ShlomiNoach
Functions: awk cat

Multi-word parameters in my.cnf can be written with either hyphens or underscores. innodb_file_per_table is the same as innodb-file-per-table, as well as innodb_file-per_table. The script normalizes the parameter names to using underscores only, keeping from changing values (e.g. ?mysql-bin? parameter value should not change).

cat my.cnf | sed '/^#/d' | sed '/^$/d' | sed -e 's/[ \t]\+//g'
cat /etc/issue
2011-06-22 15:04:45
User: h3nr1x
Functions: cat

Another way of do it in debian like distros, don't know if works for others

if [ -x /etc/*-release ]; then cat /etc/*-release ; else cat /etc/*-version ; fi
cat /etc/*-release
cat > file.txt << EOF
2011-06-18 17:00:38
User: ThePCKid
Functions: cat

This command should be the first file-editing command for a newbie. It clears file.txt (cat), and asks for input until EOF is entered on its own line (not written to file.txt).