Bash

Some useful terminal commands

Command/Key Description
grep -i Case insensitive search
grep -r Recursive search
grep -v Inverted search
grep -C <num> print <num> lines before and after the match line
cmd 1>&2 stdout to same place as stderr
cmd 2>&1 stderr to same place as stdout
!! Repeat last command
!abc Run last command starting with abc
head -n1 /etc/issue Show distribution
CTRL-a Go to the start of line
CTRL-e Go the the end of line
CTRL-u Cut from start of line
CTRL-k Cut to end of line
Ctrl + w delete from cursor to start of word (i.e. delete backwards one word)
Ctrl + y paste word or text that was cut using one of the deletion shortcuts (such as the one above) after the cursor
Ctrl + xx move between start of command line and current cursor position (and back again)
Ctrl + r search the history backwards
Ctrl + g escape from history searching mode
Ctrl + p previous command in history (i.e. walk back through the command history)
Ctrl + n next command in history (i.e. walk forward through the command history)
CTRL-d Log out from a shell (similar to exit). EOF (end-of-file). This also terminates input form stdin.
CTRL-l clear the terminal screen
CTRL-z Sleep program
bg Run the sleep program at background
fg Bring the program from background to foreground
! ! run last command
!blah run the most recent command that starts with ‘blah’ (e.g. !ls)
!blah:p print out the command that !blah would run (also adds it as the latest command in the command history)
!$ the last word of the previous command (same as Alt + .)
!$:p print out the word that !$ would substitute
!* the previous command except for the last word (e.g. if you type ‘find some_file.txt /‘, then !* would give you ‘find some_file.txt‘)
!*:p print out what !* would substitute

Remove bed file name: rm – -badfilename

Reference Cards

IF/ELIF/ELSE/FI

if [ "$animal" == "penguin" ]; then
  echo "Hmmmmmm fish... Tux happy!"
elif [ "$animal" == "dolphin" ]; then
  echo "Pweetpeettreetppeterdepweet!"
else
  echo "*prrrrrrrt*"
fi

Check comand return value

/pagh/script.sh
case $? in
  1)
    echo "return 1"
    ;;
  2)
    echo "return 2"
    ;;
  *)
    echo "return $?"
    ;;
esac

Integer comparison

Operator Description Example & comments
-eq is equal to if [ “$a” -eq “$b” ]
-ne is not equal to if [ “$a” -ne “$b” ]
-gt is greater than if [ “$a” -gt “$b” ]
-ge is greater than or equal to if [ “$a” -ge “$b” ]
-lt is less than if [ “$a” -lt “$b” ]
-le is less than or equal to if [ “$a” -le “$b” ]
< is less than (within double parentheses) ((“$a” < “$b”))
<= is less than or equal to (within double parentheses) ((“$a” <= “$b”))
> is greater than (within double parentheses ((“$a” > “$b”))
>= is greater than or equal to (within double parentheses) ((“$a” >= “$b”))

String comparison

Operator Description Example & comments
= is equal to if [ “$a” = “$b” ]
Note the whitespace framing the =.
if [ “$a”=”$b” ] is NOT equivalent to the above.
== is equal to if [ “$a” == “$b” ]
There is a synonym for =.
The == comparison operator behaves differently within a double-brackets test than with in single brackets.
[[ $a == z* ]] # True if $a starts with an “z” (pattern matching)
[[ $a == “z*” ]] # True if $a is equal to z* (literal matching)
[ $a == z* ] # File globbing and word splitting take place.
[ “$a” == “$z” ] # True if $a is equal to z* (literal matching)
!= is not equal to if[ “$a” != “$b” ]
This operator uses pattern matching with in a [[ … ]] construct.
< is less than, in ASCII alphabetical order if [[ “$a” < “$b” ]]
if [ “$a” < “$b” ]
Note that the “<” needs to be escaped within a [ … ] construct.
> is great than, in ASCII alphabetical order if [[ “$a” > “$b” ]]
if [ “$a” > “$b” ]
Note that the “>” needs to be escaped within a [ … ] construct.
-z string is null, that is, has zero length String=’’ # Zero-length (“null”) string variable.
if [ -z “$String” ]
-n strint is not null  

Special Shell Variable

Variable Meaning
$0 Filename of script
$1 Positional parameter #1
$2 - $9 Positional parameters #2 - #9
${10} Positional parameter #10
$# Number of positional parameters
”$*” All the positional parameters (as a single word) *
[email protected] All the positional parameters (as separate strings)
${#*} Number of positional parameters
${#@} Number of positional parameters
$? Return value
$$ Process ID (PID) of script
$- Flags passed to script (using set)
$_ Last argument of previous command
$! Process ID (PID) of last job run in background

Files test operators

Operator Tests Whether —– Operator Tests Whether
-e File exists   -s File is not zero size
-f File is a regular file      
-d File is a directory   -r File has read permission
-h File is a symbolic link   -w File has write permission
-L File is a symbolic link   -x File has execute permission
-b File is a block device      
-c File is a character device   -g sgid flag set
-p File is a pipe   -u suid flag set
-S File is a socket   -k “sticky bit” set
-t File is associated with a terminal      
         
-N File modified since it was last read   F1 -nt F2 File F1 is newer than F2
-O You own the file   F1 -ot F2 File F1 is older than F2
-G Group id of file same as yours   F1 -ef F2 Files F1 and F2 are hard links to the same file
         
! NOT (inverts sense of above tests)      

Reference: http://tldp.org/LDP/abs/html/