How can I replace a command line argument with tab

Question

I'm wondering if this is possible in Bash, but I'd like to use tab completion to completely replace the current argument that's being expanded. I'll give an example: I'd like to have a function that moves up an arbitrary number of levels in the tree, so I can call up 2 And that would cd me 2 directories up. However, I would like to make it so that if at the number 2, I press tab, it will expand that number to being the path (either relative or absolute, either is fine). I have this almost working using the complete builtin except it will only append the text, so it will be something like up 2/Volumes/Dev/

Is it possible to replace the completed symbol?

Thanks in advance :)

Update:

So a big thanks to chepner, because actually checking my code revealed where my bug was. I was comparing against the wrong var, and the debug code I had was causing the value to not replace.

For anyone interested, here's the code (and there could be a much better way to accomplish this):

# Move up N levels of the directory tree
# Or by typing in some dir in the PWD
# eg. Assuming your PWD is "/Volumes/Users/natecavanaugh/Documents/stuff"
#     `up 2` moves up 2 directories to "/Volumes/Users/natecavanaugh"
#     `up 2/` and pressing tab will autocomplete the dirs in "/Volumes/Users/natecavanaugh"
#     `up Users` navigate to "/Volumes/Users"
#     `up us` and pressing tab will autocomplete to "/Volumes/Users"
function up {
    dir="../"
    if [ -n "$1" ]; then
        if [[ $1 =~ ^[0-9]+$ ]]; then
            strpath=$( printf "%${1}s" );
            dir=" ${strpath// /$dir}"
        else
            dir=${PWD%/$1/*}/$1
        fi
    fi

    cd $dir
}

function _get_up {
    local cur
    local dir
    local results
    COMPREPLY=()
    #Variable to hold the current word
    cur="${COMP_WORDS[COMP_CWORD]}"

    local lower_cur=`echo ${cur##*/} | tr [:upper:] [:lower:]`

    # Is the arg a number or number followed by a slash
    if [[ $cur =~ ^[0-9]+/? ]]; then
        dir="../"
        strpath=$( printf "%${cur%%/*}s" );
        dir=" ${strpath// /$dir}"

        # Is the arg just a number?
        if [[ $cur =~ ^[0-9]+$ ]]; then
            COMPREPLY=($(compgen -W "${dir}"))
        else
            if [[ $cur =~ /.*$ ]]; then
                cur="${cur##*/}"
            fi

            results=$(for t in `cd $dir && ls -d */`; do if [[ `echo $t | tr [:upper:] [:lower:]` == "$lower_cur"* ]]; then echo "${t}"; fi done)

            COMPREPLY=($(compgen -P "$dir" -W "${results}"))
        fi
    else
        # Is the arg a word that we can look for in the PWD
        results=$(for t in `echo $PWD | tr "/" "\n"`; do if [[ `echo $t | tr [:upper:] [:lower:]` == "$lower_cur"* ]]; then echo "${t}"; fi; done)

        COMPREPLY=($(compgen -W "${results}"))
    fi  
}

#Assign the auto-completion function _get for our command get.
complete -F _get_up up

Answer 1

The following builds on the OP's own code in the question and:

• improves robustness: handles directory names that need \-escaping - e.g., names with embedded spaces - correctly; reports an error if an invalid directory name is specified (without completion)
• modifies the command-completion approach: on command completion, the level number/name prefix expands to the corresponding absolute path with a terminating /, so that further completion based on subdirectories can be performed right away, if desired.

The modified examples are:

# Assume that the working directory is '/Users/jdoe/Documents/Projects/stuff'.
#  `up 2` moves 2 levels up to '/Users/jdoe/Documents'
#  `up 2<tab>` completes to `up /Users/jdoe/Documents/`
#     Hit enter to change to that path or [type additional characters and]
#     press tab again to complete based on subdirectories.
#  `up Documents` or `up documents` changes to '/Users/jdoe/Documents'
#  `up Doc<tab>` or `up doc<tab>` completes to `up /Users/jdoe/Documents/`
#     Hit enter to change to that path or [type additional characters and]
#     press tab again to complete based on subdirectories.
#     Note: Case-insensitive completion is only performed if it is turned on
#     globally via the completion-ignore-case Readline option
#     (configured, for instance, via ~/.inputrc or /etc/inputrc).

Here's the complete code (note that the syntax coloring suggests malformed code, but that's not the case):

# Convenience function for moving up levels in the path to the current working directory.
# Synopsis:
#     `up [n]` moves n levels up in the directory hierarchy; default is 1.
#     `up dirname` changes to the closest ancestral directory by that name, regardless of case.
#     `up absolutepath` changes to the specified absolute path; primarily used with command completion (see below).
# Additionally, if command completion via _complete_up() is in effect (<tab> represents pressing the tab key):
#      `up [n]<tab>` replaces n with the absolute path of the directory n levels up (default is 1).
#      `up dirnameprefix<tab>` replaces dirnameprefix with the absolute path of the closest ancestral directory whose name starts with the specified name prefix, terminated with '/'.
#         Whether dirnameprefix is matched case-insensitively or not depends on whether case-insensitive command completion is turned on globally via ~/.inputrc or /etc/inputrc.
#       In both cases the completed absolute path ends in '/', allowing you to optionally continue completion based on that path's subdirectories.
# Notes:
#   - Directory names with characters that need escaping when unquoted (such as spaces) are handled correctly.
#   - For command completion, to specify names that need escaping when unquoted, specify them escaped rather than quoted;
#     e.g., `up my \di<tab>' to match 'my dir' in the ancestral path.
function up {

    local dir='../'   # By default, go up 1 level.

    [[ "$1" == '-h' || "$1" == '--help' ]] && { echo -e "usage:\n\t$FUNCNAME [n]\n\t$FUNCNAME dirname\n  Moves up N levels in the path to the current working directory, 1 by default.\n  If DIRNAME is given, it must be the full name of an ancestral directory (case does not matter).\n  If there are multiple matches, the one *lowest* in the hierarchy is changed to." && return 0; }

    if [[ -n "$1" ]]; then
        if [[ $1 =~ ^[0-9]+$ ]]; then   # A number, specifying the number of levels to go up.            
            local strpath=$( printf "%${1}s" ) # This creates a string with as many spaces as levels were specified.
            dir=${strpath// /$dir}  # Create the go-up-multiple-levels cd expression by replacing each space with '../'
        elif [[ $1 =~ ^/ ]]; then  # Already an absolute path? Use as is. (Typically, this happens as a result of command-line completion invoked via _complete_up().)
            dir=$1
        else # Assumed to be the full name of an ancestral directory (regardless of level), though the case needn't match.
            # Note: On case-insensitive HFS+ volumes on a Mac (the default), you can actually use case-insensitive names with 'cd' and the resulting working directory will be reported in that case(!).
            #       This behavior is NOT related to whether case-insensitivity is turned on for command completion or not.
            # !! Strangely, the 'nocasematch' shopt setting has no effect on variable substitution, so we need to roll our own case-insensitive substitution logic here.
            local wdLower=$(echo -n "$PWD" | tr '[:upper:]' '[:lower:]')
            local tokenLower=$(echo -n "$1" | tr '[:upper:]' '[:lower:]')
            local newParentDirLower=${wdLower%/$tokenLower/*}   # If the specified token is a full ancestral directory name (irrespective of case), this substitution will give us its parent path.
            [[ "$newParentDirLower" == "$wdLower"  ]] && { echo "$FUNCNAME: No ancestral directory named '$1' found." 1>&2; return 1; }
            local targetDirPathLength=$(( ${#newParentDirLower} + 1 + ${#tokenLower} ))
            # Get the target directory's name in the exact case it's defined.
            dir=${PWD:0:$targetDirPathLength}
        fi
    fi

    # Change to target directory; use of 'pushd' allows use of 'popd' to return to previous working directory.
    pushd "$dir" 1>/dev/null
}

# Companion function to up(), used for command completion.
# To install it, run (typically in your bash profile):
# `complete -o filenames -F _complete_up up`
# Note: The '-o filenames' option ensures that:
#   (a) paths of directories returned via $COMPREPLY leave the cursor at the terminating "/" for potential further completion
#   (b) paths with embeddes spaces and other characters requiring \-escaping are properly escaped.
function _complete_up {

    COMPREPLY=() # Initialize the array variable through which completions must be passed out.

    # Retrieve the current command-line token, i.e., the one on which completion is being invoked.
    local curToken=${COMP_WORDS[COMP_CWORD]}
    # Remove \ chars., presumed to be escape characters in the current token, which is presumed to be *unquoted*. This allows invoking completion on a token with embedded space, e.g., '$FUNCNAME some\ directory'
    # !! Strictly speaking, we'd have to investigate whether the token was specified with quotes on the command line and, if quoted,  NOT unescape. Given that the purpose of this function is expedience, we
    # !! assume that the token is NOT quoted and that all backslashes are therefore escape characters to be removed.
    curToken=${curToken//'\'}

    if [[ $curToken =~ ^/ ]]; then # Token is an absolute path (typically as a result of a previous completion) -> complete with directory names, similar to 'cd' (although the latter, curiously, also completes *file* names).

        local IFS=$'\n' # Make sure that the output of compgen below is only split along lines, not also along spaces (which the default $IFS would do).
        COMPREPLY=($(compgen -o dirnames -- "$curToken"))

    elif [[ $curToken =~ ^[0-9]+/? ]]; then # Token is a number (optionally followed by a slash) -> replace the token to be completed with the absolute path of the directory N levels above, where N is the number specified.

        # Create a go-up-multiple-levels cd expression that corresponds to the number of levels specified.
        local strpath=$( printf "%${curToken%%/*}s" ) # This creates a string with as many spaces as levels were specified.
        local upDirSpec=${strpath// /../}  # Create the go-up-multiple-levels cd expression by replacing each space with '../'        

        # Expand to absolute path (ending in '/' to facilitate optional further completion) and return.
        local dir=$(cd "$upDirSpec"; echo -n "$PWD/")
        if [[ "$dir" == '//' ]]; then dir='/'; fi # In case the target dir turns out to be the root dir, we've accidentally created '//' in the previous statement; fix it.
        # !! Note that the path will appear *unquoted* on the command line and must therefore be properly \-escaped (e.g., a ' '  as '\ ').
        # !! Escaping is performed automatially by virtue of defining the compspec with '-o filenames' (passed to 'complete').
        COMPREPLY=("$dir") 

    else # Token is a name -> look for a prefix match among all the ancestral path components; use the first match found (i.e., the next match up in the hierarchy).

        # Determine if we should do case-insensitive matching or not, depending on whether cases-insensitive completion was turned on globally via ~/.inputrc or /etc/inputrc.
        # We do this to be consistent with the default command completion behavior.
        local caseInsensitive=0        
        bind -v | egrep -i '\bcompletion-ignore-case[[:space:]]+on\b' &>/dev/null && caseInsensitive=1

        # If we need to do case-INsensitive matching in this function, we need to make sure the 'nocasematch' shell option is (temporarily) turned on.
        local nocasematchWasOff=0
        if (( caseInsensitive )); then
            nocasematchWasOff=1
            shopt nocasematch >/dev/null && nocasematchWasOff=0
            (( nocasematchWasOff )) && shopt -s nocasematch >/dev/null
        fi

        local pathSoFar=''
        local matchingPath=''
        # Note: By letting the loop iterate over ALL components starting at the root, we end up with the *last* match, i.e. the one *lowest* in the hierarchy (closed to the current working folder).
        # !! We COULD try to return multiple matches, if applicable, but in practice we assume that there'll rarely be paths whose components have identical names or prefixes.
        # !! Thus, should there be multiple matches, the user can reinvoke the same command to change to the next-higher match (though the command must be typed again), and so forth.
        local parentPath=${PWD%/*}
        local IFS='/' # This will break our parent path into components in the 'for' loop below.
        local name
        for name in ${parentPath:1}; do
            pathSoFar+=/$name
            if [[ "$name" == "$curToken"* ]]; then
                matchingPath="$pathSoFar/"
            fi
        done

        # Restore the state of 'nocasematch', if necessary.
        (( caseInsensitive && nocasematchWasOff )) && shopt -u nocasematch >/dev/null

        # If match was found, return its absolute path (ending in / to facilitate optional further completion).
        # !! Note that the path will appear *unquoted* on the command line and must therefore be properly \-escaped (e.g., a ' '  as '\ ').
        # !! Escaping is performed automatially by virtue of defining the compspec with '-o filenames' (passed to 'complete').
        [[ -n "$matchingPath" ]] && COMPREPLY=("$matchingPath")

    fi  
}

# Assign the auto-completion function for up().
complete -o filenames -F _complete_up up

Answer 2

It is possible to completely replace the current word with a single new word. With my bash 4.2.29, I can do this:

_xxx() { COMPREPLY=( foo ); }
complete -F _xxx x
x bar # pressing tab turns this into x foo

You encounter problems, however, if there is more than one possible completion, and you want to get partial completion of the common prefix. Then my experiments indicate that bash will try to match the available completions to the prefix you entered.

So in general you should probably only replace the current argument with something completely different if that something is uniquely defined. Otherwise, you should generate completions which match the current prefix, to have the user select from those. In your case you could replace the COMPREPLY=($(compgen -P "$dir" -W "${results}")) with something along these lines:

local IFS=$'\n'
COMPREPLY=( $(find "${dir}" -maxdepth 1 -type d -iname "${cur#*/}*" -printf "%P\n") )
if [[ ${#COMPREPLY[@]} -eq 1 ]]; then
    COMPREPLY=( "${dir}${COMPREPLY[0]}" )
fi

However, in this specific case it might be better to only replace the prefix digit by the appropriate path, and leave everything else to the default bash completion:

_up_prefix() {
    local dir cur="${COMP_WORDS[COMP_CWORD]}"
    COMPREPLY=()

    if [[ ${cur} =~ ^[0-9]+/? ]]; then
        # Starting with a number, possibly followed by a slash
        dir=$( printf "%${cur%%/*}s" );
        dir="${dir// /../}"
        if [[ ${cur} == */* ]]; then
            dir="${dir}${cur#*/}"
        fi
        COMPREPLY=( "${dir}" "${dir}." ) # hack to suppress trailing space
    elif [[ ${cur} != */* ]]; then
        # Not a digit, and no slash either, so search parent directories
        COMPREPLY=( $(IFS='/'; compgen -W "${PWD}" "${cur}") )
        if [[ ${#COMPREPLY[@]} -eq 1 ]]; then
            dir="${PWD%${COMPREPLY[0]}/*}${COMPREPLY[0]}/"
            COMPREPLY=( "${dir}" "${dir}." ) # hack as above
        fi
    fi
}

complete -F _up_prefix -o dirnames up

The code becomes a lot easier to read and maintain, plus more efficient to boot. The only drawback is that in some cases you'd have to press tab one more time than you used to: once to substitute the prefix, and twice more to actually see the list of possible completions. Your choice whether that's acceptable.

One more thing: the completion will turn the argument into a regular path, but your up function as it is does not accept those. So perhaps you should start that function with a [[ -d $1 ]] check, and simply cd to that directory if it exists. Otherwise your completion will generate arguments which are unacceptable to the called function.