for loop in bash

Question

I want to create a for loop that runs from 1 to a number stored in a variable. But it produces this error:

Syntax error: Bad for loop variable

This is my script:

#!/bin/bash

count_lines () 
{
  local f=$1  
  l=`wc -l $f | sed 's/^\([0-9]*\).*$/\1/'`
}
echo "$0 counts the lines of code" 
l=0
while [ "$*" != ""  ]
do
        count_lines $1
        echo "$1: $l"
        shift
done
for(( i= 0 ; i <= ${l} ; i++))
do
   title=$(grep -oPm1 "(?<=<title>)[^<]+" <<< "$0")
   echo "$title"
done

Answer 1

Make sure that the script is executable, and run the script by just typing the command, including its path. For example, if the script is called foo and is in the current directory, run

./foo

Given the error message, you are doing something like sh foo. This runs the script under sh, not bash. sh on your machine is a different shell, probably dash, which doesn't support the for loop syntax you used. By running ./foo, your script will be executed by the shell mentioned in the first line, which is bash.

Your script is weird in several places:

• Always put double quotes around variable substitutions: "$1", "$f", etc.

• That while [ "$*" != "" ] … loop is a very roundabout way of iterating over the arguments of the script. The simple, idiomatic way is

  for x; do
    count_lines "$x"
  done
  

  or

  for x in "$@"; do
    count_lines "$x"
  done
  

• I'm not sure what you're trying to do with title=$(grep -oPm1 "(?<=<title>)[^<]+" <<< "$0"); "$0" is the path to the script, so you're searching the regexp (?<=<title>)[^<]+ in the path to the script, which doesn't make much sense.

Answer 2

The main problem I believe is with not testing if the file actually exists and getting a count l that is invalid for the for loop.

Take a look at this (very modified) similar script to give you some ideas:

#!/bin/bash

count_lines() {
if [[ -r $1 ]]; then     # if the file exist.
  l="$(wc -l "$1")"      # count the number of lines.
  l="${l%%[^0-9]*}"      # remove anything that is not a digit from the end.
else
  l=0
fi
}
echo "$0 counts the lines of code"

for file; do               # while there is an argument.
  count_lines "$file"    # execute the function above
  echo "$file: $l"       # print the number of lines.
done

echo "$(grep -oPm1 "(?<=<title>)[^<]+" "$0")"

I can not understand why you try to run l times a command (grep) to find title inside a file. One time is enough.

Also, the grep command is reading the script (not an external file).

As Gilles said: heavily correct your code, post a new question.