Relative paths based on file location instead of current working directory

Question

Given   some txt dir   -cat sh   With cat sh having the content   cat    some txt   Then running   cat sh inside dir works fine while running   dir cat sh on the same level as dir does not  I expect this to be due to the different working directories  Is there an easy way to make the path    some txt relative to the location of cat sh

User · Accepted Answer

What you want to do is get the absolute path of the script (available via ${BASH_SOURCE[0]}) and then use this to get the parent directory and cd to it at the beginning of the script.

#!/bin/bash
parent_path=$( cd "$(dirname "${BASH_SOURCE[0]}")" ; pwd -P )

cd "$parent_path"
cat ../some.text

This will make your shell script work independent of where you invoke it from. Each time you run it, it will be as if you were running ./cat.sh inside dir.

Note that this script only works if you're invoking the script directly (i.e. not via a symlink), otherwise the finding the current location of the script gets a little more tricky)

User · Answer

Just one line will be OK   cat   dirname  0      some txt

User · Answer

Martin Konecny s answer provides the correct answer  but - as he mentions - it only works if the actual script is not invoked through a symlink residing in a different directory   This answer covers that case  a solution that also works when the script is invoked through a symlink or even a chain of symlinks     Linux   GNU readlink solution   If your script needs to run on Linux only or you know that GNU readlink is in the  PATH  use readlink -f  which conveniently resolves a symlink to its ultimate target    scriptDir   dirname --    readlink -f --   BASH SOURCE       Note that GNU readlink has 3 related options for resolving a symlink to its ultimate target s full path  -f  --canonicalize   -e  --canonicalize-existing   and -m  --canonicalize-missing  - see man readlink  Since the target by definition exists in this scenario  any of the 3 options can be used  I ve chosen -f here  because it is the most well-known one     Multi- Unix-like- platform solution  including platforms with a POSIX-only set of utilities    If your script must run on any platform that    has a readlink utility  but lacks the -f option  in the GNU sense of resolving a symlink to its ultimate target  - e g   macOS    macOS uses an older version of the BSD implementation of readlink  note that recent versions of FreeBSD PC-BSD do support -f   does not even have readlink  but has POSIX-compatible utilities - e g   HP-UX  thanks   Charles Duffy     The following solution  inspired by https   stackoverflow com a 1116890 45375  defines helper shell function  rreadlink    which resolves a given symlink to its ultimate target in a loop - this function is in effect a POSIX-compliant implementation of GNU readlink s -e option  which is similar to the -f option  except that the ultimate target must exist   Note  The function is a bash function  and is POSIX-compliant only in the sense that only POSIX utilities with POSIX-compliant options are used  For a version of this function that is itself written in POSIX-compliant shell code  for  bin sh   see here    If readlink is available  it is used  without options  - true on most modern platforms  Otherwise  the output from ls -l is parsed  which is the only POSIX-compliant way to determine a symlink s target  Caveat  this will break if a filename or path contains the literal substring - gt  - which is unlikely  however   Note that platforms that lack readlink may still provide other  non-POSIX methods for resolving a symlink  e g    Charles Duffy mentions HP-UX s find utility supporting the  l format char  with its -printf primary  in the interest of brevity the function does NOT try to detect such cases   An installable utility  script  form of the function below  with additional functionality  can be found as  rreadlink in the npm registry  on Linux and macOS  install it with  sudo  npm install -g rreadlink  on other platforms  assuming they have bash   follow the manual installation instructions    If the argument is a symlink  the ultimate target s canonical path is returned  otherwise  the argument s own canonical path is returned      usr bin env bash    Helper function  rreadlink       execute function in a  subshell  to localize the effect of  cd          local target  1 fname targetDir readlinkexe   command -v readlink  CDPATH        Since we ll be using  command  below for a predictable execution     environment  we make sure that it has its original meaning       unalias command   unset -f command     amp  gt  dev null    while    do   Resolve potential symlinks until the ultimate target is found           -L  target    -e  target         command printf   s n    FUNCNAME  ERROR    target  does not exist    gt  amp 2  return 1          command cd    command dirname --   target      Change to target dir  necessary for correct resolution of target path        fname   command basename --   target     Extract filename            fname            amp  amp  fname         curiously   basename    returns           if    -L  fname     then           Extract  next  target path  which is defined           relative to the symlink s own directory          if    -n  readlinkexe     then   Use  readlink             target     readlinkexe  --   fname           else    readlink  utility not available              Parse  ls -l  output  which  unfortunately  is the only POSIX-compliant              way to determine a symlink s target  Hypothetically  this can break with             filenames containig literal   - gt    and embedded newlines            target   command ls -l --   fname             target   target   - gt            fi         continue   Resolve  next  symlink target        fi       break   Ultimate target reached    done   targetDir   command pwd -P    Get canonical dir  path     Output the ultimate target s canonical path      Note that we manually resolve paths ending in    and     to make sure we     have a normalized path    if     fname            then     command printf   s n     targetDir       elif      fname             then       Caveat  something like  var    will resolve to  private  assuming        var  - gt   private var   i e  the      is applied AFTER canonicalization      command printf   s n     command dirname --    targetDir       else     command printf   s n     targetDir     fname    fi      Determine ultimate script dir  using the helper function    Note that the helper function returns a canonical path  scriptDir   dirname --    rreadlink   BASH SOURCE

[bash] Relative paths based on file location instead of current working directory

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