How to check whether a string starts with a substring

Question

I am writing a very simple script which copies a file to a path provided by the user as a parameter and I would like to make sure the path starts with /var/log/messages.

So I've written this:

if [[ $2 -ne /var/log/messages/* ]]
then
  echo "Incorrect path, must be under /var/log/messages/"
  exit
fi

But it doesn't seem to work.

What am I doing wrong?

You can do [[ $2 != /var/log/messages/* ]] (incorrect path) — Maroun
– Maroun, Commented Apr 27, 2015 at 12:53

Jahid · Accepted Answer · 2015-04-27 12:54:56Z

4

This should work:

if [[ "$2" != "/var/log/messages/"* ]]
then
  echo "Incorrect path, must be under /var/log/messages/"
  exit
fi

answered Apr 27, 2015 at 12:54

Jahid

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Comments

thevilledev · Accepted Answer · 2015-04-28 12:33:17Z

2

You can use regular expressions as well (starting from Bash version 3). Just remember this:

Every quoted part of the regular expression is taken literally, even if it contains regular expression special characters.

In this case, you could do something like this:

if [[ ! "$2" =~ ^"/var/log/messages/" ]]
then
   echo "Incorrect path, must be under /var/log/messages/"
   exit
fi

answered Apr 28, 2015 at 12:33

thevilledev

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Comments

user1794469 · Accepted Answer · 2015-04-27 12:59:38Z

1

You should in general provide a minimal non-working example. However, I suspect you want:

if [[ $2 != /var/log/messages/* ]]
then
  echo "Incorrect path, must be under /var/log/messages/"
  exit
fi

answered Apr 27, 2015 at 12:59

user1794469

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Comments

chown · Accepted Answer · 2015-04-27 12:55:05Z

0

You could use dirname:

if [[ `dirname $2` != "/var/log/messages" ]]
then
  echo "Incorrect path, must be under /var/log/messages/"
  exit
fi

answered Apr 27, 2015 at 12:55

chown

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2 Comments

user4453924 Over a year ago

This doesn't account for subdirectories.

chown Over a year ago

This is true, I thought he wanted to make sure that $2 was in /var/log/messages only

Marty McGowan · Accepted Answer · 2015-04-27 18:36:26Z

0

UNTESTED:

...
case $2 in
/var/log/messages/*) ;;
    # do whatever...
*)
    echo "incorrect ..."
    break
    ;;
esac
...

answered Apr 27, 2015 at 18:36

Marty McGowan

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