Bash: iterate from last to first member of an array [duplicate] - bash

Question

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Is there a way to get the git root directory in one command?
(22 answers)
Closed 2 years ago.
I'm attempting to find the "root" of a folder. I'm doing this in a Bash script with the following (at least in my head):
# Get current directory (e.g. /foo/bar/my/subdir)
CURR_DIR = `cwd`
# Break down into array of folder names
DIR_ARRAY=(${CURR_DIR//\// })
# Iterate over items in DIR_ARRAY starting with "subdir"
<HELP WITH FOR LOOP SYNTAX>
# Each loop:
# build path to current item in DIR_ITER; e.g.
# iter N: DIR_ITER=/foo/bar/my/subdir
# iter N-1: DIR_ITER=/foo/bar/my
# iter N-2: DIR_ITER=/foo/bar
# iter 0: DIR_ITER=/foo
# In each loop:
# get the contents of directory using "ls -a"
# look for .git
# set ROOT=DIR_ITER
export ROOT
I've Googled for looping in Bash but it all uses the "for i in ARRAY" form, which doesn't guarantee reverse iteration order. What's the recommended way to achieve what I want to do?

Answer 1

One idea on reverse index referencing.
First our data:
$ CURR_DIR=/a/b/c/d/e/f
$ DIR_ARRAY=( ${CURR_DIR//\// } )
$ typeset -p DIR_ARRAY
declare -a DIR_ARRAY=([0]="a" [1]="b" [2]="c" [3]="d" [4]="e" [5]="f")
Our list of indices:
$ echo "${!DIR_ARRAY[#]}"
0 1 2 3 4 5
Our list of indices in reverse:
$ echo "${!DIR_ARRAY[#]}" | rev
5 4 3 2 1 0
Looping through our reverse list of indices:
$ for i in $(echo "${!DIR_ARRAY[#]}" | rev)
do
echo $i
done
5
4
3
2
1
0
As for working your way up the directory structure using this 'reverse' index strategy:
$ LOOP_DIR="${CURR_DIR}"
$ for i in $(echo "${!DIR_ARRAY[#]}" | rev)
do
echo "${DIR_ARRAY[${i}]}:${LOOP_DIR}"
LOOP_DIR="${LOOP_DIR%/*}"
done
f:/a/b/c/d/e/f
e:/a/b/c/d/e
d:/a/b/c/d
c:/a/b/c
b:/a/b
a:/a
Though we could accomplish the same thing a) without the array and b) using some basic parameter expansions, eg:
$ LOOP_DIR="${CURR_DIR}"
$ while [ "${LOOP_DIR}" != '' ]
do
subdir="${LOOP_DIR##*/}"
echo "${subdir}:${LOOP_DIR}"
LOOP_DIR="${LOOP_DIR%/*}"
done
f:/a/b/c/d/e/f
e:/a/b/c/d/e
d:/a/b/c/d
c:/a/b/c
b:/a/b
a:/a

Answer 2

You can use dirname in a loop, to find the parent folder, then move up until you e.g., find the .git folder.
Quick example:
#!/usr/bin/env bash
set -eu
for arg in "$#"
do
current=$arg
while true
do
if [ -d "$current/.git" ]
then
echo "$arg: .git in $current"
break
fi
parent="$(dirname "$current")"
if [ "$parent" == "$current" ]
then
echo "No .git in $arg"
break
fi
current=$parent
done
done
For each parameter you pass to this script, it will print where it found the .git folder up the directory tree, or print an error if it didn't find it.