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Argument Variables

Variable References
$# number of command-line arguments given.
$? exit value of the last command that was executed.
$0 the command run by the user ( zeroth argument ).
$x x’th argument of the command, eg $1, $2.
$* all the arguments ($1 $2 …). when quoted, single string.
$@ all the arguments, when quoted, individual strings (“$1” “$2” …).
$$ process number for shell or script executing.
$! process number of the last background command.

History

  • use ctrl-r to reverse search history semi-interactively
  • history 10: print 10 histroy items
  • !<something>:p print without executing
cmd arg  arg  arg  arg
    !^             !$
    |----- !* -------|
|------- !! ---------|
Variable References
!! last command
!baz last command that starts with baz
!?baz last command containing baz
!300 history item 300
!$ the last argument of the previous command
!^ first arg of prev command
!:2 second arg of prev command
!* all arguments of the last command

Directory containing script 

DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"

Switch case 

case $1 in
  --help)
    usage
    ;;
  string)
    someFlag=1
    ;;
  opt|other)
    two options
    ;;
  *)
    unmatched stuff
esac

Loop 

for i in $(seq 1 7); do

done

# not portable
for i in {1..7}; do
done

# update command progress
for pc in $(seq 1 100); do
  sleep 1
  echo -ne "updating $pc%\r"
done

Colorized output 

$(tput setaf 1) <text here> $(tput sgr0) # Standard colors
\[\e[0;32m\]  <this is in color 0;32>  \[\e[m\] # Any color

Standard colors:

  • 1 red
  • 2 green
  • 3 yellow
  • 4 blue
  • 5 purple
  • 6 light
  • 7 white

Template with argument parsing

This script will set flags based on args, then treat the first real arg as a filename. Or, read from stdin if no real arg is provided

# Show usage and exit if no arguments.
if [ "$#" = 0 ]; then
  echo usage
fi

# Parse options.
while :; do
  case $1 in
    --help)
      usage
      ;;
    --someFlag)
      someFlag=1
      ;;
    *) break
  esac
  shift
done

# Get the content from FILENAME or stdin.
content="$(cat "${1:-/dev/stdin}")"

Template for task automation

To bootstrap an automation script, start with just asking the user to complete all steps. Gradually replace steps with actual automation, as nessesary.

#! /bin/bash

echo -n "--> Please do step 1 "
read

echo -n "--> Please do step 2 "
read

echo “Finished”

Heredocs

Heredocs are used to include a document in place. The contents will be passed to a command via stdin.

The delimeter is traditionally EOF, but any string can be used if EOF appears in the contents.

Placing quotes around the starting delimiter (<<'EOF') will prevent variable substitution in the contents.

Basic form

_command_ <<EOF
multi line
long text block
EOF

Often used for a script’s help information.

cat <<EOF
usage information: $0
-a  arg one
-b  arg two
EOF

cat <<EOF > ./file.txt
some stuff
EOF

Single line variation

_command_ <<<"single line string"
# Equivalent to:
echo "single line string" | _command_

Conditionals

Flag True if file …
-a, -e exists
-r is readable
-w is writable
-x is exists and is executable
-O is owned by the effective user ID
-G is owned by the effective group ID
-d is a directory
-f is a regular file
-h, -L is a symbolic link
-S is a socket
-b is a block-special
-c is a character-special
-p is a named pipe,
-N is modified since read
-g has its SGID bit set,-k sticky bit is set
-s has a size greater than zero
-u has its SUID bit set
-t descriptor is open refers to a terminal
Operator Meaning
-nt left changed more recently than right
-ot left is older than right
-et left and right have the same inode
-z length of string is zero
-n length of string is non-zero
== strings equal
!= strings not equal
< left string sorts before right string
-eq -ne -lt -le -gt -ge integer comparison
! not
-a and
-o or