Bash – How to Use Awk Scripts on the Path

If you don't already have duplicates in the PATH and you only want to add directories if they are not already there, you can do it easily with the shell alone.

for x in /path/to/add …; do
  case ":$PATH:" in
    *":$x:"*) :;; # already there
    *) PATH="$x:$PATH";;
  esac
done

And here's a shell snippet that removes duplicates from $PATH. It goes through the entries one by one, and copies those that haven't been seen yet.

if [ -n "$PATH" ]; then
  old_PATH=$PATH:; PATH=
  while [ -n "$old_PATH" ]; do
    x=${old_PATH%%:*}       # the first remaining entry
    case $PATH: in
      *:"$x":*) ;;          # already there
      *) PATH=$PATH:$x;;    # not there yet
    esac
    old_PATH=${old_PATH#*:}
  done
  PATH=${PATH#:}
  unset old_PATH x
fi

I'll join the other advice that you shouldn't parse the output of ls, so this is a bad example. But as a more general matter, I would include the awk script directly in the shell script by passing it as an argument to awk.

#!/bin/bash
ls -lhF "$@" | awk '
    ( NF >= 9 ) {
        print "|-- [" $5 "] " $9
    }'

Note that if the awk script must include the ' (single quote) character, you need to quote it: use '\'' (close single quote, literal single quote, open single quote).

To avoid having to quote, you can use a here document instead. But it's awkward because you can't use standard input both to feed input to awk and to feed the script. You need to use an additional file descriptor (see When would you use an additional file descriptor? File descriptors & shell scripting).

#!/bin/bash
ls -lhF "$@" | awk -f /dev/fd/3 3<<'EOF'
( NF >= 9 ) {
    print "|-- [" $5 "] " $9
}
EOF

Inside awk, you can read input from another command using the getline function and the pipe construct. It's not the way awk is primarily designed to be used, but it can be made to work. You need to quote the file name arguments for the underlying shell, which is highly error-prone. And since the text to be processed doesn't come from the expected sources (standard input or the files named on the command line), you end up with all the code in the BEGIN block.

#!/usr/bin/awk -f
BEGIN {
    command = "ls -lhF"
    for (i = 1; i <= ARGC; i++) {
        arg = ARGV[i];
        gsub("'", "'\\''", arg);
        command = command " '" arg "'";
    }
    ARGC = 0; for (i in ARGV) delete ARGV[i];
    while ((command | getline) > 0) {
        if (NF >= 9) { print "|-- [" $5 "] " $9 }
    }
}

In short, use a shell for what it's good at (such as piping commands together), and awk for what it's good at (such as text processing).