concise bash script to replace filename in absolute path

Question

I need concise and readable function to be used in bash script which will take as input:

• absolute path (e.g. /home/user/tmp/data/sample1.txt )
• new filename name (e.g. extended_sample.dat )

and return

absolute path with new filename (e.g. /home/user/tmp/data/extended_sample.dat )

Thank you in advance!

Answer 1

There's 2+1(bonus) commands that make life easy with dealing with path names:

• basename - strip directory and suffix from filenames

• dirname - strip last component from file name

• readlink - print resolved symbolic links or canonical file names

So to answer your question:

old_path=/home/user/tmp/data/sample1.txt
new_file=extended_sample.dat

new_path="$(dirname $old_path)/$new_file"

Or to change the path name of the original file:

alt_path=/mnt/newroot/foo

new_path="$alt_path/$(basename $old_path)"

Extract full location of the running script (works if the script is executed off its own file):

dirname $(readlink -f ${0})

With these 3 commands you can do most of your path manipulations easily.

Answer 2

Note, the return statement in bash functions is used to return a numeric value as a status code.

How it may look in most simple case:

#!/bin/bash

path="/home/user/tmp/data/sample1.txt"
new_name="extended_sample.dat"

function get_new_path() { echo "${1%/*}/$2"; }

new_path=$(get_new_path "$path" "$new_name")
echo "$new_path"

The above will output:

/home/user/tmp/data/extended_sample.dat

Answer 3

Just playing around with bash namerefs:

path_replace_file () {
    local -n pathvar="$1"
    pathvar="${pathvar%/*}/$2"
}

pathname="/home/user/tmp/data/sample1.txt"

printf 'pathname before = %s\n' "$pathname"
path_replace_file pathname extended_sample.dat
printf 'pathname after  = %s\n' "$pathname"

Output:

pathname before = /home/user/tmp/data/sample1.txt
pathname after  = /home/user/tmp/data/extended_sample.dat

The path_replace_file function takes a variable name as its first argument. In the function pathvar acts like an alias (a name reference) for that variable.

The function replaces the filename portion of the value of $pathval with whatever is given as the second argument to the function.

This requires bash 4.3 or later.

Changing local -n to typeset -n will make it work in ksh93 too.