Bash Notes

BashNotes.md

Bash notes

bash -n : test syntax without running the script shopt -s extglob : turns on extra glob features of the shell (for regexp tests) set -o noclobber - prevents overwriting files

General

• {} : groups a series of commands.
• () : groups a series of commands and executes them in a subshell
• $() - the newer syntax for ``
• $(( )) : lets you do arithmatic inside

• | - will overwrite a file even with noclobber on

• <</EOF - prevents evaluating variables
• read -p "your prompt" variable
• $? - the exit status of the last command run
• cmd1 && cmd2 && cmd3 - will shortcircuit if the previous command fails
• nohup - ignores hangup from closing a bash shell (for running headless cmds)
• env is a subset of set
• let y+=3 : won't echo result

Params being passed

• ${1} - first arg
• $* - all arguments
• $@ - all args quoted?
• ${#} - the number of args

grep

• grep -l : prints filenames only
• grep -v : the stuff to ignore (grep "whatever" file | grep -v "but ignore this pattern")

comparisons

testing numbers

[ 4 -lt 5 -a 6 -eq 6 ]

• comparisons: -lt, -eq, -ne, -ge, etc.
• booleans: -a (and), -o (or)

testing strings

[ '4' == '4' -a '6' != '5' ]

• comparisons: ==, !=, >, <=, etc.

[[ ]] - more powerful comparison, not supported in older shells

find

• find --follow : will follow simlinks
• find --iname : case insensitive filenames