mjhjmtu

I am trying to open a file through a script; as long as I pass the file as the first argument there are no problems; for instance:

$ cat textExample.txt 
Much I marvelled this ungainly fowl to hear discourse so plainly,
Though its answer little meaning- little relevancy bore;
For we cannot help agreeing that no living human being
Ever yet was blessed with seeing bird above his chamber door-
Bird or beast upon the sculptured bust above his chamber door,
With such name as "Nevermore."
$ ./tester.sh textExample.txt 
BEGIN PROGRAM
parse file
For we cannot help agreeing that no living human being

where tester.sh is written like this:

#!/bin/bash

# options
optstring=fh
Feature=0
Help=0
while getopts $optstring opt
do
 case $opt in
 f) Feature=1;;
 h) Help=1 ;;
 *) echo WRONG && exit 1 ;;
 esac
done

if [[ $Feature == 1 ]] ; then
 echo "This is a feature of the program"
elif [[ $Help == 1 ]] ; then
 echo "This is the help page"
fi

echo "BEGIN PROGRAM"
# assign file name
file=$1
echo "parse file"
grep 'cannot help' $file

exit 0

Only the -h flag works because there is an exit statement:

$ ./tester.sh -h
This is the help page
$ ./tester.sh -f
This is a feature of the program
BEGIN PROGRAM
parse file
grep: option requires an argument -- 'f'
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.

Therefore, I modified the script introducing a step to check if the argument is a flag:

#!/bin/bash

# options
optstring=fh
Feature=0
Help=0
while getopts $optstring opt
do
 case $opt in
 f) Feature=1;;
 h) Help=1 ;;
 n) Custom_name=$OPTARG ;;
 *) echo WRONG && exit 1 ;;
 esac
done

if [[ $Feature == 1 ]] ; then
 echo "This is a feature of the program"
elif [[ $Help == 1 ]] ; then
 echo "This is the help page"
 exit
fi

for i in $@ ; do
 if [[ "$i" =~ "-" ]] ; then
 true
 else
 input=$i
 fi
done


echo "BEGIN PROGRAM"
# assign file name
echo "parse file"
grep 'cannot help' $input

exit 0

and the result is:

$ ./tester.sh -f
This is a feature of the program
BEGIN PROGRAM
parse file
$ ./tester.sh -f textExample.txt 
This is a feature of the program
BEGIN PROGRAM
parse file
For we cannot help agreeing that no living human being

The problem is: if I add another argument to save the line to a file of a name of choice, I have another problem. Modifying the file in:

#!/bin/bash

# options
optstring=fhn:
Feature=0
Help=0
output=
while getopts $optstring opt
do
 case $opt in
 f) Feature=1;;
 h) Help=1 ;;
 n) output=$OPTARG ;;
 *) echo WRONG && exit 1 ;;
 esac
done

if [[ $Feature == 1 ]] ; then
 echo "This is a feature of the program"
elif [[ $Help == 1 ]] ; then
 echo "This is the help page"
 exit
fi

for i in $@ ; do
 if [[ "$i" =~ "-" ]] ; then
 true
 else
 input=$i
 fi
done


echo "BEGIN PROGRAM"
# assign file name
echo "parse file"
if [[ -z $output ]] ; then
 grep 'cannot help' $input
else
 grep 'cannot help' $input > $output
fi

exit 0

the output is:

$ ./tester.sh -f textExample.txt 
This is a feature of the program
BEGIN PROGRAM
parse file
For we cannot help agreeing that no living human being
$ ./tester.sh -f -n my_file textExample.txt 
This is a feature of the program
BEGIN PROGRAM
parse file
$ ./tester.sh -n my_file textExample.txt 
BEGIN PROGRAM
parse file

That is: there is no input file anymore, bash is looking at the argument my_file as the input file.

I have been thinking to bracket the output file in single or double quotes and check for their presence, but I can't escape the quote, thus I get an error. Modifying the section:

for i in $@ ; do
 if [[ "$i" =~ "-" ]] ; then
 true
 elif [[ "$i" =~ ' ]] ; then
 true
 else
 input=$i
 fi
done

I get:

$ ./tester.sh -n 'my_file' textExample.txt 
BEGIN PROGRAM
parse file

That is, bash does not recognize the quotes in the argument. I tried different options such as "'", ''' etc as well as $i, "$i".

Is there a way to check the presence of quotes in an argument?
Or a better way to handle arguments?

After processing the options with getopts, the variable OPTIND is set to the index of the first non-option argument, so do this:

while getopts $optstring opt; do
 #... 
done
# now, remove the options from the positional parameters
shift $((OPTIND-1))

Now, $1 contains the filename.