How to customize bash
InstallFest 2017

Invocation Options

-l / --login

login shell

--noprofile

--init-file ⬚

ommit / use file

--norc

--rcfile ⬚

omit / use file

-r / --restricted

restricted shell

-v / --verbose

verbose mode

--posix

$POSIXLY_CORRECT

set -o posix

POSIX compatible mode

Logout

cat ~/.bash_logout
# ~/.bash_logout: executed by bash(1) when
# login shell exits. When leaving the console
# clear the screen to increase privacy.

if [ "$SHLVL" = 1 ]; then
   [ -x /usr/bin/clear_console ] &&
      /usr/bin/clear_console -q
fi

Set Options 2

• -e / -o errexit

  foo
  [shell exits]      

• -r / -o noglob

  echo /*
  /*

• -k / -o keyword

  a=1 bash -c 'declare -p a b' b=2
  declare -x a="1"
  declare -x b="2"

Set Options 3

• -B / -o braceexpand

  echo {01..20..2}
  01 03 05 07 09 11 13 15 17 19

• -H / -o histexpand

  !!
  echo {01..20..2}
  01 03 05 07 09 11 13 15 17 19

Set Options 4

• -C / -o noclobber

  > foo
  > foo
  bash: foo: cannot overwrite existing file

• -o ignoreeof

  IGNOREEOF=2
  Ctrl + d
  Use "exit" to leave the shell.
  Use "exit" to leave the shell.

Set Options 5

• -u / -o nounset

  : $a $b $c; foo
  bash: a: unbound variable

• -t / -o onecmd

  pwd; sleep 5
  /tmp
  [shell exits after 5 seconds]

Set Options 6

• -P / -o physical

  ln -s ~ /tmp/h
  cd /tmp/h/.. ; pwd
  /home

• -o pipefail

  grep :/var/ruuun/ /etc/passwd | wc -l
  0
  echo $?
  1

Set Options 7

• -x / -o xtrace

  echo $(( $(echo $(( $(date +%s) + 3600)) \
           | wc -c ) - 1))
  ++ wc -c
  +++ date +%s
  ++ echo 1488498282
  + echo 10
  10

• -o vim / -o emacs

Shell Options 2

• cmdhist — bash attempts to save all lines of a multiple-line command in the same history entry

  while sleep 1; do
     date
  done
  while sleep 1; do date; done

• direxpand

  foo=/var/tmp
  ls $foo tab ls /var/tmp

Shell Options 3

• dirspell

  cd /tpm/ tab cd /tmp/

• dotglob

  echo *
  .aptitude .bash_history .bash_logout
  .bashrc .blender ...

• expand_aliases

Shell Options 4

• extglob

  rm img+([0-9]).jpg
  rm img!(+([0-9]).jpg
  rm img*.@(jpg|png|gif)

• failglob

  echo fi*le
  bash: no match: fi*le

Shell Options 5

• force_fignore — suffixes specified by the $FIGNORE cause words to be ignored

FIGNORE=.swp:.tmp:~
ls tab

• globasciiranges

  touch {a..z} {A..Z}
  echo [a-z]
  a b c d ...

Shell Options 6

• globstar

  mkdir -p /var/tmp/a/b/c
  file /var/tmp/a/**
  /var/tmp/a/:    directory
  /var/tmp/a/b:   directory
  /var/tmp/a/b/c: directory

Shell Options 7

• histappend — history list is appended to the file, rather than overwriting the file
• histverify — resulting line is loaded into the readline editing buffer, allowing further modification
• lithist — multi-line commands are saved to the history with embedded newlines rather than using semicolons

Shell Options 8

• nocaseglob

  echo .v*
  .vim .viminfo .viminfz.tmp .vimrc .VirtualBox

• nullglob

  mkdir tmp
  echo tmp/*

Shell Options 9

• progcomp — programmable completion facilities are enabled
• xpg_echo

  echo 'a\nb'
  a
  b

Shell Variables 1

• $BASH_CMDS[] (unsetting element has no effect)

  BASH_CMDS+=([d]=/usr/bin/date)
  BASH_CMDS[grep]=/usr/xpg4/bin/grep
  hash
  hits    command
  2       /usr/xpg4/bin/grep
  0       /usr/bin/date
  1       /usr/bin/man

Shell Variables 2

• $BASH_XTRACEFD

  exec 3>/dev/pts/4
  BASH_XTRACEFD=3
  set -x

• $CDPATH

  CDPATH=~/Project:/var/www/vhosts
  cd if17
  /home/barinkl/Project/if17

Shell Variables 3

• $EXECIGNORE — (patterns) ignored by command search (completion), except in hash table

  EXECIGNORE=*/bz*:*grep*

• $FCEDIT

  FCEDIT=vim
  fc

Shell Variables 4

• $FIGNORE — suffices ignored by filename completion

  FIGNORE='~:.bak:.tmp'

• $GLOBIGNORE — suffices ignored by globbing

  GLOBIGNORE=*.bak:*.tmp

Shell Variables 5

• $HISTCONTROL — second and subsequent lines of a multi-line compound command are not tested

  HISTCONTROL=ignorespace:ignoredups:erasedups

• $HISTFILE, $HISTFILESIZE, $HISTSIZE

  # /dev/null disables saving history
  HISTFILE=~/.bash_history
  HISTSIZE=500
  HISTFILESIZE=$HISTSIZE

Shell Variables 6

• $HISTIGNORE — (patterns) ignored by history
  (& = suppresses duplicate entries)

  HISTIGNORE="&:ls:[bf]g:exit:[ \t]*"

• $HISTTIMEFORMAT — adds #TIMESTAMP into history file

  HISTTIMEFORMAT='%Y-%m-%d %T'

Shell Variables 7

• $IFS — (patterns) ignored by history
  (& = suppresses duplicate entries)

  IFS=:
  while read user:pass:uid:gid:comm:home:shell
  do ...
  done < /etc/passwd
  IFS=$' \t\n'

• $TMOUT — timeout for read, select and shell

Shell Variables 8

• $LANG, $LC_*
  • sorting the results of pathname expansion
  • range expressions
  • character classes
  • equivalence classes
  • collating sequences
  • number formatting
  • data and time formatting

touch {a..z} {A..Z} é ch
export LC_ALL=en_US.utf8
ls [a-z]* | tr -d '\n'
aAbBcCchdDeEéfFg...yYz

export LC_ALL=C
ls [a-z]* | tr -d '\n'
abcchdefghijklmnopqrstuvwxyz

export LC_COLLATE=cs_CZ.utf8 LC_CTYPE=cs_CZ.utf8
ls [[:lower:]]* | tr -d '\n'
abcdeéfghchijklmnopqrstuvwxyz

Shell Variables 9

• $PS0 — after reading a command and before the command is executed

  PS0='\e[01;40;33m\
  $(printf "%${COLUMNS}s" \!)\e[0m\n'

• $PS1 — primary prompt
• $PS2 — secondary prompt
• $PS3 — prompt for the select command
• $PS4 — before each command during an execution trace

Shell Variables 10

• $PROMPT_COMMAND — value is executed as a command prior to issuing each primary prompt

  export PROMPT_COMMAND='history -a; history -n'
  PS1='\[\033]0;\u@\h:\w\007\]\u@\h:\w\$ '

• $PROMPT_DIRTRIM — number of trailing directory components to retain when expanding the \w and \W string escapes

  PROMPT_DIRTRIM=1; cd /var/log/apache2
  user@host:.../apache2 >

• $BASH_ALIASES[]

  BASH_ALIASES+=([sl]=ls [..]='cd ..')

alias c='cd '
alias p='~/Documents/Work/Projects'
c p
cd ~/Documents/Work/Projects

For almost every purpose,
aliases are superseded by shell functions.

function command_not_found_handle {
if [ -x /usr/lib/command-not-found ]
then
   /usr/lib/command-not-found -- "$1"
   return $?
elif [ -x /usr/share/command-not-found/command-not-found ]
then
   /usr/share/command-not-found/command-not-found -- "$1"
   return $?
else
   printf "%s: command not found\n" "$1" >&2
   return 127
fi
}

builtin / command

• builtin

  function cd {
     echo "From: $PWD" >&2
     builtin cd "$@"
     echo "To: $PWD" >&2
  }

builtin / command

• builtin

  function du {
     command du -sh "$@" \
     | egrep '^([0-9.]+G|([5]|1[0-9])[0-9][0-9]M)'
  }

stty — Set Teletype

stty -a | sed -n 2,4p
intr = ^C; quit = ^\; erase = ^?; kill = ^U;
   eof = ^D; eol = <undef>;
eol2 = <undef>; swtch = <undef>; start = ^Q;
   stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; discard = ^O; ...
stty intr ^T

Disown shell job

xclock &
[1] 21157
jobs
[1]+  Running                 xclock &
disown %1
jobs

PS0 and Trap on DEBUG

trap 'echo DEBUG' DEBUG
PS0=$'PS0\n'
pwd; echo .
PS0
DEBUG
/home/barinkl
DEBUG
.
DEBUG

Bind Keys to Actions

showkey -a   F2
Press any keys - Ctrl-D will terminate this ...

^[OQ   27 0033 0x1b
       79 0117 0x4f
       81 0121 0x51

Ctrl+V  F2
^[OQ

bind "\"\eOQ\":\"git commit -am ''\e[D\""
bind -x '"\ez":"date"'

Readline Configuration

set blink-matching-paren on
set expand-tilde on
set keyseq-timeout 500
"\C-t": forward-search-history
"##":   insert-comment
"\C-o": "> /dev/null"
"\ez":  "date\n"
"\eOQ": "git commit -am ''\e[D" 

finfo vs stat

time for ((i=0;i<1000;i++))
do
   finfo -m .           stat -c %Y .
done >/dev/null

   real  0m0,005s       real  0m0,768s
   user  0m0,004s       user  0m0,020s
   sys   0m0,000s       sys   0m0,164s

shared objects

finfo

display information about file attributes

realpath

display pathname in canonical form

strftime

display formatted time