Bash Script Cheat Sheet

http://steve-parker.org/sh/sh.shtml

v1.1 – 7 Aug 2007

UNIX / Linux Shell Cheat Sheet

File Manipulation

Test Operators

Variable Substitution

> file >> file >file 2>&1 < file a|b

if [ “$x” -lt “$y” ]; then # do something fi

${V:-def} ${V: ${V:=d =def ef} } ${V:?err}

Numeric Tests

Conditional Execution

lt gt eq ne ge le

c1 || c2 c1 && c2

create (overwrite) file append to file both output and errors to file read from file pipe output from 'a' as input to 'b'

Common Constructs while read f do echo “Line is $f” done < file

read text file line by line

$ grep foo myfile afoo foo foobar

less than greater than equal to not equal greater or equal less or equal

File Tests

find matching lines

$ cut -d: -f5 /etc/passwd Dilbert

get field with delimiter

foo=`ls`

get output of command

case $foo in a) echo “foo is A” ;; b) echo “foo is B” ;; *) echo “foo is not A or B” ;; esac doubleit() { expr $1 \* 2 } doubleit 3 # returns 6

case is a good way to avoid iterating through many if/elif/elif/elif   constructs.

function declaration and calling syntax

nt d f r w x

newer than is a directory is a file readable writeable executable

String Tests

= z n

equal to zero length not zero length

Logical Tests

&& || !

logical AND logical OR logical NOT

$V, or “def” if unset $V (set (set to “def “def” ” if unse unset) t) $V, or “err” if unset

run c1; if it fails, run c2 run c1; if it works, run c2

Common utilities and switches ls -lSr ls -ltr ls -lh du -sk * sort -n ps -ef wget URL time cm cmd touch file read x cmd | \ tee file.txt nice ice cmd cmd

list files, biggest last list files, newest last human-readable filesizes directory sizes (slow) sort numerically (not alpha) list  my commands download URL stopwatch on on `c `cmd` create file read “x” from keyboard cmd output to stdout and also to file.txt run cmd cmd with low priority

Networking ifconfig -a netstat -r ssh u@host scp scp file file.t .txt xt \ u@host:: u@host

list all network interfaces show routers log in to host as user “u” copy copy file file.t .txt xt to host host as user “u”

Argument Variables

General Admin

$0 $1 $2 ... $9 $* $#

less file alias l='ls -l' tar cf t.tar \ list_of_files cal 3 1973 df -h truss -p PID

program name 1st argument 2nd argument ... 9th argument all arguments No. of arguments

display file, page by page create “l” as alias for “ls -l” create a tar archive t.tar from the listed dirs/files display a calendar (Mar 73) show disk mounts show syscalls of PID

Files: Contents / Attributes for i in * do echo “File is $i” done

A for loop iterates through its input (which is subject to globbing)

find . -size 10k -print find . -name “*.txt” -print find /foo -type d -ls three=`expr 1 + 2` echo "scale = 5 ; 5121 / 1024” | bc egrep “(foo|bar)” file

Useful Variables $IFS $? $SHELL LANG

Internal File Separator return code from last program what shell ell is running this script? Language; C is US English

awk '{ print $5 }' file sed s/foo/bar/g file

files over 10Kb find text files ls all directories under /foo simple maths better maths find “foo” or “bar” in file print the 5th word of each line replace “foo” in file with “bar”

A full PDF and online tutorial is available at http://steve-parker.org/sh/sh.shtm http://steve-parker.org/sh/sh.shtmll