Shell – Check argument before program run

autocompleteshell

I have noticed that, when I type unzip in bash and press tab, auto-complete works only on files with .zip extension. How is that done? What if I would like to make program that would accept only image files, how to restrict auto-complete to certain extensions (eg .jpg and .png only).

Is this some kind of system setting or an programming setting that vary for languages (bash, C++, python) ?

Best Answer

The program itself runs whatever file names are passed to it. The restriction to a .zip suffix in completion is unrelated to what the program does. Completion is performed by the shell. When you press Tab, the shell parses the command line to some extent looks up the completion rules for the context. Depending on the shell, the context analysis and completion rules may be more or less complex. For example, when the command line contains echo $P and you press Tab, most shells with completion look for variable names beginning with P. By default, shells complete file names, because it's a very common case.

Bash, tcsh and zsh have ways to make the completion programmable: they parse the command under the cursor, and look up the rules for that particular command in a table. With programmable completion, the entry in the table for the unzip program should say that the first argument must be an existing .zip file, and subsequent arguments must be names of members of the zip archive.

The completion rules are not contained in the program itself, but they may be shipped alongside the program in the same package. For example, a package that contains a command /usr/bin/foo can contain a file /etc/bash_completion/foo that describes to bash how to complete arguments for the foo command, and a similar file /usr/share/zsh/functions/Completion/_foo for zsh.

Related Solutions

Bash – Is there a way to customize “Programmable Completion” in the current session

In the bash_completion mechanism it's the bash function _filedir_xspec() that is responsible for filename and dirname completions. This funtion can be found in the script /etc/bash_completion.

You can edit that function and add a line that contains your regex. For example use this function (it's a copy of the original function):

_filedir_xspec()
{
    local IFS cur xspec

    IFS=$'\n'
    COMPREPLY=()
    _get_comp_words_by_ref cur

    _expand || return 0

    # get first exclusion compspec that matches this command
    xspec=$( awk "/^complete[ \t]+.*[ \t]${1##*/}([ \t]|\$)/ { print \$0; exit }" \
        "$BASH_COMPLETION" )
    # prune to leave nothing but the -X spec
    xspec=${xspec#*-X }
    xspec=${xspec%% *}

    local -a toks
    local tmp

    toks=( ${toks[@]-} $(
        compgen -d -- "$(quote_readline "$cur")" | {
        while read -r tmp; do
            # see long TODO comment in _filedir() --David
            printf '%s\n' $tmp
        done
        }
        ))

    # Munge xspec to contain uppercase version too
    eval xspec="${xspec}"
    eval xspec="!*.txt" #<---- HERE add your regex, that's the only line changed
    local matchop=!
    if [[ $xspec == !* ]]; then
        xspec=${xspec#!}
        matchop=@
    fi
    [[ ${BASH_VERSINFO[0]} -ge 4 ]] && \
        xspec="$matchop($xspec|${xspec^^})" || \
        xspec="$matchop($xspec|$(printf %s $xspec | tr '[:lower:]' '[:upper:]'))"

    toks=( ${toks[@]-} $(
        eval compgen -f -X "!$xspec" -- "\$(quote_readline "\$cur")" | {
        while read -r tmp; do
            [ -n $tmp ] && printf '%s\n' $tmp
        done
        }
        ))
    [ ${#toks[@]} -ne 0 ] && _compopt_o_filenames
    COMPREPLY=( "${toks[@]}" )
}

Notice the new part at line 32:

eval xspec="!*.txt"

This statement is later used in compgen to remove all entries, that do not match the regular expression. I wouldn't recommend to edit the file /etc/bash_completion. Instead make a new file with the content above and source the file if needed:

source /path/to/file

Now, all commands/applications in the shell, that where completed by the function _filedir_xspec(), complete now only with *.txt filenames.

Bash autocomplete with vim command

I did some more research for you and here is what I found - the key to autocompletion is the bash command complete. You can print the rules for vim using:

complete -p vim

Likewise you can remove these specific rules with:

complete -r vim

This command resets it to defaults - the usual paths and file names completion without any extra logic. That's probably what you want.

For more info check out help complete or man bash and look for the section about complete command (it's a bash built-in, hence it's documented in the bash manpage).

One last point - the above changes only affect the current bash session, if you want to remove the vim rules after every login put the complete -r vim to your ~/.bashrc.

Hope that helps :)

Best Answer

Related Solutions

Bash – Is there a way to customize “Programmable Completion” in the current session

Bash autocomplete with vim command

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