Check If Shell Script $1 Is Absolute Or Relative Path [duplicate] - bash

Question

This question already has answers here:
Determine if relative or absolute path in shell program
(4 answers)
Closed 6 years ago.
As the title says, I am trying to determine if my bash script receives a full path or a relative file to a directory as a parameter.
For some reasons the following doesn't seem to work for me:
#!/bin/bash
DIR=$1
if [ "$DIR" = /* ]
then
echo "absolute"
else
echo "relative"
fi
When I run my script with either a full path or absolute path it says:
./script.sh: line 5: [: too many arguments
relative
For some reasons I can't seem to figure this bug. Any ideas?

Answer 1

[ ... ] doesn't do pattern matching. /* is being expanded to the contents of /, so effectively you have
if [ "$DIR" = /bin /boot /dev /etc /home /lib /media ... /usr /var ]
or something similar. Use [[ ... ]] instead.
if [[ "$DIR" = /* ]]; then
For POSIX compliance, or if you just don't have a [[ that does pattern matching, use a case statement.
case $DIR in
/*) echo "absolute path" ;;
*) echo "something else" ;;
esac

Answer 2

Just test on the first character:
if [ "${DIR:0:1}" = "/" ]

Answer 3

One more case is paths started from ~ (tilde). ~user/some.file or ~/some.file are some kind of absolute paths.
if [[ "${dir:0:1}" == / || "${dir:0:2}" == ~[/a-z] ]]
then
echo "Absolute"
else
echo "Relative"
fi

Answer 4

ShellCheck automatically points out that "[ .. ] can't match globs. Use [[ .. ]] or grep."
In other words, use
if [[ "$DIR" = /* ]]
This is because [ is a regular command, so /* is expanded by the shell beforehand, turning it into
[ "$DIR" = /bin /dev /etc /home .. ]
[[ is handled specially by the shell, and doesn't have this problem.

Answer 5

Writing tests is fun:
#!/bin/bash
declare -a MY_ARRAY # declare an indexed array variable
MY_ARRAY[0]="/a/b"
MY_ARRAY[1]="a/b"
MY_ARRAY[2]="/a a/b"
MY_ARRAY[3]="a a/b"
MY_ARRAY[4]="/*"
# Note that
# 1) quotes around MY_PATH in the [[ ]] test are not needed
# 2) the expanded array expression "${MY_ARRAY[#]}" does need the quotes
# otherwise paths containing spaces will fall apart into separate elements.
# Nasty, nasty syntax.
echo "Test with == /* (correct, regular expression match according to the Pattern Matching section of the bash man page)"
for MY_PATH in "${MY_ARRAY[#]}"; do
# This works
if [[ $MY_PATH == /* ]]; then
echo "'$MY_PATH' is absolute"
else
echo "'$MY_PATH' is relative"
fi
done
echo "Test with == \"/*\" (wrong, becomes string comparison)"
for MY_PATH in "${MY_ARRAY[#]}"; do
# This does not work at all; comparison with the string "/*" occurs!
if [[ $MY_PATH == "/*" ]]; then
echo "'$MY_PATH' is absolute"
else
echo "'$MY_PATH' is relative"
fi
done
echo "Test with = /* (also correct, same as ==)"
for MY_PATH in "${MY_ARRAY[#]}"; do
if [[ $MY_PATH = /* ]]; then
echo "'$MY_PATH' is absolute"
else
echo "'$MY_PATH' is relative"
fi
done
echo "Test with =~ /.* (pattern matching according to the regex(7) page)"
# Again, do not quote the regex; '^/' would do too
for MY_PATH in "${MY_ARRAY[#]}"; do
if [[ $MY_PATH =~ ^/[:print:]* ]]; then
echo "'$MY_PATH' is absolute"
else
echo "'$MY_PATH' is relative"
fi
done