How to get first character of variable

Question

I'm trying to get the first character of a variable, but I'm getting a Bad substitution error. Can anyone help me fix it?

code is:

while IFS=$'\n' read line
do
  if [ ! ${line:0:1} == "#"] # Error on this line
  then
    eval echo "$line"
    eval createSymlink $line
  fi
done < /some/file.txt

Am I doing something wrong or is there a better way of doing this?

-- EDIT --

As requested - here's some sample input which is stored in /some/file.txt

$MOZ_HOME/mobile/android/chrome/content/browser.js
$MOZ_HOME/mobile/android/locales/en-US/chrome/browser.properties
$MOZ_HOME/mobile/android/components/ContentPermissionPrompt.js

Answer 1

To get the first character of a variable you need to say:

v="hello"
$ echo "${v:0:1}"
h

However, your code has a syntax error:

[ ! ${line:0:1} == "#"]
#                     ^-- missing space

So this can do the trick:

$ a="123456"
$ [ ! "${a:0:1}" == "#" ] && echo "doesnt start with #"
doesnt start with #
$ a="#123456"
$ [ ! "${a:0:1}" == "#" ] && echo "doesnt start with #"
$ 

Also it can be done like this:

$ a="#123456"
$ [ "$(expr substr $a 1 1)" != "#" ] && echo "does not start with #"
$ 
$ a="123456"
$ [ "$(expr substr $a 1 1)" != "#" ] && echo "does not start with #"
does not start with #

Update

Based on your update, this works to me:

while IFS=$'\n' read line
do
  echo $line
  if [ ! "${line:0:1}" == "#" ] # Error on this line
  then
    eval echo "$line"
    eval createSymlink $line
  fi
done < file

Answer 2

Adding the missing space (as suggested in fedorqui's answer ;) ) works for me.

An alternative method/syntax

Here's what I would do in Bash if I want to check the first character of a string

if [[ $line != "#"* ]]

On the right hand side of ==, the quoted part is treated literally whereas * is a wildcard for any sequence of character.

For more information, see the last part of Conditional Constructs of Bash reference manual:

When the ‘==’ and ‘!=’ operators are used, the string to the right of the operator is considered a pattern and matched according to the rules described below in Pattern Matching

Checking that you're using the right shell

If you are getting errors such as "Bad substitution error" and "[[: not found" (see comment) even though your syntax is fine (and works fine for others), it might indicate that you are using the wrong shell (i.e. not Bash).

So to make sure you are using Bash to run the script, either

• make the script executable and use an appropriate shebang e.g. #!/bin/bash
• or execute it via bash my_script

Also note that sh is not necessarily bash, sometimes it can be dash (e.g. in Ubuntu) or just plain ol' Bourne shell.