How to Get Bash Script’s Own Path

Posted on by Eric Ma In Programming, Tutorial

Bash script may need to get its own path. In normal Bash script, $0 is the path to the script. However, when a script is sourced, such as . a.sh, a.sh‘s $0 does not give a.sh while the caller’s name. How to reliably get a bash script’s own path no matter whether the Bash script is executed or sourced is introduced in this post.

Short answer

You can use ${BASH_SOURCE[0]} to get the script’s own path, in sourced or directly executed Bash script.

Why ${BASH_SOURCE[0]} contains the own path

From bash manual:

BASH_SOURCE
An array variable whose members are the source filenames where the corresponding shell function names in the FUNCNAME array variable are defined. The shell function ${FUNCNAME[$i]} is defined in the file ${BASH_SOURCE[$i]} and called from ${BASH_SOURCE[$i+1]}.

What about ${BASH_SOURCE[0]? This following example shows it well.

We have 2 Bash scripts: a.sh and b.sh which is sourced by a.sh and contains a function.

a.sh

#!/bin/bash

echo "\$0: $0"

echo ${FUNCNAME[0]} in ${BASH_SOURCE[0]}

. ./b.sh

b.sh

#!/bin/bash

echo "\$0: $0"

echo ${FUNCNAME[0]} in ${BASH_SOURCE[0]}

fun() {
    echo ${FUNCNAME[0]} in ${BASH_SOURCE[0]}
    echo $0
}

fun

What happens if we run a.sh directly by sh a.sh?

The result is as follows.

$0: a.sh
main in a.sh
$0: a.sh
source in ./b.sh
fun in ./b.sh
a.sh

What about we source a.sh by . a.sh instead of executing it? It gives

$0: bash
source in a.sh
$0: bash
source in ./b.sh
fun in ./b.sh
bash

In summary, in sourced or directly executed bash script files, ${BASH_SOURCE[0] contains the path of the bash source file and ${FUNCNAME[0] contains “source” or “main”. So, ${BASH_SOURCE[0]} gives you a reliable variable for the Bash script source file path no matter whether it is used inside of a function and no matter whether the script is directed executed or sourced.

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Eric Ma

Eric is a systems guy. Eric is interested in building high-performance and scalable distributed systems and related technologies. The views or opinions expressed here are solely Eric's own and do not necessarily represent those of any third parties.

4 comments 

  1. 
//A c function to get your own executable's execution directory. 
// Sometimes you want to know the program source 

#ifndef MAX_PATH
#define MAX_PATH 256
#endif

static char * get_path_to_me(void);
static char *
get_path_to_me ()
{
    static char buffer[MAX_PATH];
    char *cp;
    int len;
    if ((len = readlink ("/proc/self/exe", buffer, sizeof (buffer) - 1)) != -1)
    {
        buffer[len] = '\0';
        cp=strrchr(buffer,'/');
        *cp='\0';
        fprintf (stderr, "\n%s version 0.9, date Compiled: %s, ", cp+1, __DATE__);
        fprintf (stderr, "is executed from %s\n", buffer);      //program executes, dirname ok
        *cp='/';
    }
    else
        *buffer = '\0';
    return (buffer);
}
#if 0             // set to 1 to test as stand-alone, leave  as 0 if you want to include this function in your code.
/**
 * @brief main
 * @param argc
 * @param argv
 * @return
 */
int
main (int argc, char *argv[])
{
    char *pgm;
    char *pgmx;
    pgm = strdup (get_path_to_me ());
    strcpy(buffer,pgm);
    printf("\nfull path = %s, directory=%s program=%s\n",buffer,dirname(pgm),basename(pgm));
    return 0;
}
#endif
    Reply

    1. Thanks for sharing the C code.

      This is a nice trick:

      readlink (“/proc/self/exe”, buffer, sizeof (buffer) – 1)

      Reply

  2. This is awesome.

    I still don’t completely understand it,
    but I definitely understand it better than before
    and I have a lot to learn about bash fundamentals anyway.

    Thanks for the write-up!

    Reply

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