bash

Bash: variable from commands

To assign the output of a command into a bash variable:

var=$(command)

Bash: passing environment variables

For environment variables to be visible from within a bash script, you must export them.

Given the bash script:

#!/bin/bash
echo $myvar

The environment variable myvar must be set this way:

$ myvar="test"; # This won't work.
$ export myvar="test"; # This works.

Another solution would be to source another script where those variables are defined.
You may source in a sub-shell in order to limit the scope of the variables:

( . ./all_my_variables.sh )

~/.bashrc

The ~/.bashrc file is a bash configuration file.
It is read when starting a new X session provided that bash is set as the default shell.

See also:
http://linux.overshoot.tv/home/user/.xinitrc
http://linux.overshoot.tv/home/user/.xprofile

bash: working with directories

Sample code: check if directory exists, if not, create it. Check if the directory is writable.

if test ! -d "$MYDIR"
then
  mkdir "$MYDIR"
elif test ! -w "$MYDIR"
then
  echo "$MYDIR exists but is not writable."
  exit 3
fi

konsole: Warning: Could not start program '/bin/bash' with arguments '/bin/bash'.

Sat, 04/01/2017 - 03:43 - augustin

Sometimes, when I start a KDE session where konsole instances are being restored, I find in one of the konsole tabs:

Warning: Could not start program '/bin/bash' with arguments '/bin/bash'.
Warning: No such file or directory
Warning: Could not start program '/bin/bash' with arguments '/bin/bash'.
Warning: No such file or directory

The problem is temporary. Other tabs are ok. I close the affected tab and open a new one without problems.

bash, man command completion

Fri, 10/28/2016 - 02:03 - augustin

What drives command completion (tab) in bash?

When I want: man rc-update and type man rc and then TAB, I don't get command completion.

Where is my PS1 defined?

Thu, 02/11/2016 - 11:29 - augustin

When I chroot into my gentoo environment, PS1 is defined but I don't know where.

$ sudo chroot /mnt/gentoo
# echo $PS1
\[\033]0;\u@\h:\w\007\]\[\033[01;31m\]\h\[\033[01;34m\] \W \$\[\033[00m\]
/ # env-update && source /etc/profile
>>> Regenerating /etc/ld.so.cache...
# echo $PS1
\[\033]0;\u@\h:\w\007\]\[\033[01;31m\]\h\[\033[01;34m\] \W \$\[\033[00m\]

I greped but couldn't find where that PS1 was defined...

Find out where alias was set

Tue, 02/09/2016 - 16:15 - augustin

If I do:
$ alias my_aliased_command
I can find out which command the alias stands for.
e.g.

$ alias ll
alias ll='ls -lh --color=always'
$ alias lla
alias lla='ls -lha'
$ alias la
alias la='ls -A --color=always'

Is there a way to discover we might have set up on our system but forgotten (or simply didn't know about)?

I'd like to be able to do:

$ alias --reverse ls
alias la='ls -A --color=always'
alias lla='ls -lha'
alias ll='ls -lh --color=always'

No manual entry for alias

Tue, 02/09/2016 - 16:10 - augustin

$ man alias
No manual entry for alias

=> There should be one.

Not all bash builtin commands have their man page

Sat, 01/23/2016 - 09:24 - augustin

Having man pages for bash builtin commands is convenient.
man echo provides the man page for the bash command 'echo'.

Some/most builtin commands do not have their own man page.
e.g. man read give man 2 read, which is about a c++ library. There is no man page for man 1 read (bash's read).

The official bash documentation is unwieldy.

Currently, my info pages are broken: #5475: The Info node shell builtin commands in Info file /usr/share/info/bash.info does not exist.

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