Command-Line – Can I Edit a Bash Shell Command?

14.04bashcommand linegnome-terminal

I just wants to modify a bash shell command like exit so when i write exit in the terminal it clears the screen, and echo some text, wait 2 seconds, then execute the exit function.
So is there any way to modify a shell command on Ubuntu, if there is away how ?

Best Answer

You can use a shell alias

alias exit='clear; sleep 2; exit'

To make it permanent, add the alias to the bottom of the ~/.bashrc file. see this thread for help

Related Solutions

Ubuntu – iPython Like Command History For Shell

Bash does have that feature too, but it's not enabled by default. You can bind it to cursor up/down by sticking this into ~/.inputrc:

"\e[A": history-search-backward
"\e[B": history-search-forward

I prefer to bind it to Ctrl+up/down instead:

"\e[1;5A": history-search-backward
"\e[1;5B": history-search-forward

edit: To preserve ctrl+left and ctrl+right for moving back and forward in whole words, also include these lines in ~/.inputrc file:

# mappings for Ctrl-left-arrow and Ctrl-right-arrow for word moving
"\e[1;5C": forward-word
"\e[1;5D": backward-word
"\e[5C": forward-word
"\e[5D": backward-word
"\e\e[C": forward-word
"\e\e[D": backward-word

Ubuntu – Bash – executing commands in current shell

To exec or not to exec

a call to exec replaces a shell's data, and therefore the shell can't return from an exec system call.

But not every command is the name of a program to execute. So often there is no exec call involved. The key distinction is that in contrast to ( cmd1; cmd2; ), you don't get another shell process. Or perhaps more correctly, the shell will only fork to execute child programs, not to execute shell processes.

Strange prompt

what does the command line belong.

As other answers have pointed out, your command was incomplete. So the command line belonged to bash itself, which was waiting for the end of your group.

Uses

Also, how is executing commands in the current shell in any way useful?

… as opposed to subshell grouping

The most prominent example is setting variables in that subcommand. Thy this:

foo=1; { foo=2; echo $foo; }; ( foo=3; echo $foo; ); echo $foo

This will print

2
3
2

So although you set foo=3 inside one group, that group was executed in a subshell and its settings didn't propagate to the parent.

Another thing worth considering is current working directory. { cd foo; make; } will leave you in directory foo whereas ( cd foo; make; ) will not alter the current working directory of your main shell.

… as opposed to ungrouped commands

The grouping is mostly useful if you have other code outside, e.g. conditionals

test -f foo && { echo "Foo exists."; rm foo; }

or redirections

{ echo "Content of $PWD:"; ls; } | gzip > dirlist.gz