Flag argument is another flag - bash

Trying to read my flag and their arguments,
I came accros a case where passing a flag with an expected argument,
fallowed by another flag instead of the expected argument,
would result in the second flag being interpreted as argument for the first flag.
WWW_ALIAS=0
while getopts ':d:a:w' flag; do
case "${flag}" in
d)
DOMAIN_NAME=${OPTARG}
;;
a)
IFS=',' read -ra DOMAIN_ALIASES <<< "${OPTARG}"
;;
w)
WWW_ALIAS=1
;;
:)
echo "[Error] Argument for option -${OPTARG} was omitted." 1>&2
exit 1
;;
\?)
echo "[Warning] Option ${OPTARG} is not supported and will be ignored." 1>&2
;;
esac
done
if [ -z "${DOMAIN_NAME}" ]; then
echo "[Error] Domain parameter (-d) must be set" 1>&2
exit 1
fi
Thus, running ./script.sh -w -d will trigger the error message at the end of this code example.
But running ./script.sh -d -w will instead assign -w to the DOMAIN_NAME variable while it shouldn't.
Is there a way to make sure that any flag can't be used as argument for a flag ?

The supported syntax for getopts is:
a - option -a without value; error on unsupported options
a: - option -a with value; error on unsupported options
ab - check for options -a, -b; error on unsupported options
:ab - check for options -a, -b; silences errors on unsupported options
Since you specified d:, the argument parser will check for an additional value after the switch -d. Not specifying one, just like in this command: ./script.sh -w -d will trigger an error from the argument parser (not your code).
Since you specified w without a (: after it), the argument parser will NOT check for an additional value after the switch -w. Hence you don't see an error for that flag.
When you run with -d -w, the parser sees only the first switch, which is -d, and it consumes the next token as the argument, which is the expected outcome.
As there a way to make sure that any flag can't be used as argument for a flag?
Yes, there are a couple of options actually.
Option 1: inside the menu, add a sanity check to allow only reasonable values:
...
case "${flag}" in
d)
if [[ "${OPTARG}" == -* ]]; then
echo "Bad argument!"
exit 1
fi
DOMAIN_NAME=${OPTARG}
;;
...
Option 2: Use eval set -- "$OPTS"
Some don't like this option because eval is evil. But it's still an option if you are not afraid of this attack vector.
This command will sort the arguments and will prevent things like this from happening.
Find an example here

Related

how to pass other arguments besides flags

I am trying to execute my file by passing in an absolute path as the first argument ($1). I also want to add flags from that absolute path onward, but i do not know how to tell optargs to start counting from $2 forward since if i pass in the absolute path as the $1 it seems to break the getopts loop.
I'm gussing i have to implement a shift for the first argument in the following code:
while getopts :lq flag; do
case $flag in
l) echo "executing -l flag"
;;
q) echo "executing -q flag"
;;
esac
done
I'm not sure how to approach this. Any tips are welcome, thank you.
getopts does, indeed, stop processing the arguments when it sees the first non-option argument. For what you want, you can explicitly shift the first argument if it is not an option. Something like
if [[ $1 != -* ]]; then
path=$1
shift
fi
while getopts :lq flag; do
...
done
Keep the options before file argument (i.e. absolute path).
Many standard bash commands follow the same practice.
Example :
wc -wl ~/sample.txt
ls -lR ~/sample_dir
So if you follow the above practice, your code goes like this.
This code works even if options are not provided.
In general, that is the desired behavior with options.
# Consider last argument as file path
INPUT_FILEPATH=${*: -1}
echo $INPUT_FILEPATH
# Process options
while getopts :lq flag
do
case $flag in
l) echo "executing -l flag"
;;
q) echo "executing -q flag"
;;
esac
done
Sample execution :
bash sample.sh /home/username/try.txt
/home/username/try.txt
bash sample.sh -lq /home/username/try.txt
/home/username/try.txt
executing -l flag
executing -q flag

Bash use getopts but enforce the options

Is possible to use getopts to force the user that run the script, to add the options?
I am not asking how to make an option to require a parameter (done with the : after the option), but how to actually tell the user that he need to add the -something when running the script.
Something like myscript.sh -f FILENAME; and if the user run the script as myscript.sh FILENAME he will get an error because he didn't add the -f option.
As now I check if $1 is empty or not, to print the usage message; and another statement to check if the -f option is in what the user passed; although if you have 10 options, you add 10 conditional statements? That feels a bit off and not efficient.
Once again, I am not asking how to handle getopts parameters, but the options themselves. I think the question is pretty clear to show that this has nothing to do with the answer mentioned as possible duplicate of this question.
Sounds like you want something like tar, which (usually) requires the user to specify an operation mode followed (usually) by the file name arguments. If that is the case, then no getopts alone will not help you. However, you can still use getopts to manage the arguments:
#!/bin/bash
help() {
cat <<EOTXT
${1:-This program does something.}
USAGE:
${0##*/} <-abcde> <thing>
WHERE:
-a Sets mode a
...
EOTXT
}
mode=0
OPTIND=1
while getopts abc opt; do
case "${opt}" in
a|b|c) mode=${opt};;
?) help "Unrecognized option"; exit 1;
esac
done
shift "$((OPTIND-1))"
[[ 0 == ${mode} ]] && { help "Missing mode: use one of -a, -b, or -c"; exit 1; }
[[ 0 == $# ]] && { help "Missing thing argument"; exit 1; }
Here you use the typical while getopts construct to process your arguments. When it detects one of your required flags, you set the bookkeeping variable ($mode here) to the value. Then at the end, you check that you have both mode and an extra argument.
Thus all of these test cases fail:
my-program # no mode or argument
my-program -a # mode, but no argument
my-program foo # argument, but no mode
my-program -d # bad mode, no argument
my-program -d foo # bad mode with argument
Only this passes:
my-program -a foo

Boolean cli flag using getopts in bash?

Is it possible to implement a boolean cli option using getopts in bash? Basically I want to do one thing if -x is specified and another if it is not.
Of course it is possible. #JonathanLeffler already pretty much gave the answer in the comments to the question, so all I'm going to do here is add an example of the implementation and a few niceties to consider:
#!/usr/bin/env bash
# Initialise option flag with a false value
OPT_X='false'
# Process all options supplied on the command line
while getopts ':x' 'OPTKEY'; do
case ${OPTKEY} in
'x')
# Update the value of the option x flag we defined above
OPT_X='true'
;;
'?')
echo "INVALID OPTION -- ${OPTARG}" >&2
exit 1
;;
':')
echo "MISSING ARGUMENT for option -- ${OPTARG}" >&2
exit 1
;;
*)
echo "UNIMPLEMENTED OPTION -- ${OPTKEY}" >&2
exit 1
;;
esac
done
# [optional] Remove all options processed by getopts.
shift $(( OPTIND - 1 ))
[[ "${1}" == "--" ]] && shift
# "do one thing if -x is specified and another if it is not"
if ${OPT_X}; then
echo "Option x was supplied on the command line"
else
echo "Option x was not supplied on the command line"
fi
A few notes about the above example:
true and false are used as option x indicators because both are valid UNIX commands. This makes the test for the option presence more readable, in my opinion.
getopts is configured to run in silent error reporting mode because it suppressed default error messages and allows for a more precise error handling.
the example includes fragments of code for dealing with missing option arguments and post-getopts command line arguments. These are not part of the OP's question.
They are added for the sake of completeness as this code will be required in any reasonably complex script.
For more information about getopts see Bash Hackers Wiki: Small getopts tutorial

Parsing a flag with a list of values

I'm creating a bash script which involves parsing arguments. The usage would be:
$ ./my_script.sh -a ARG_1 -b ARG_2 [-c LIST_OF_ARGS...]
Using getopts I'm able to parse -a and -b and get their respective values ARG_1 and ARG_2. If and only if user places -c as last argument, then I'm also able to get -c and create a list with all values in LIST_OF_ARGS....
But I would not like to force user to insert -c as the last flag. For instance, it would be great if the script can be invoked this way:
$ ./my_script.sh -b ARG_2 -c V1 V2 V3 -a ARG_1
Here is my current code:
while getopts a:b:c opt
do
case $opt in
a)
A_FLAG=$OPTARG
;;
b)
B_FLAG=$OPTARG
;;
c)
# Handle values as regular expressions
args=("$#")
C_LIST=()
for (( i=$OPTIND-1 ; i <= $#-1 ; i++ ))
do
C_LIST=("${C_LIST[#]}" ${args[$i]})
done
;;
?)
usage
;;
esac
done
You need to separate your detection of the -c flag with the processing associated with it. For example, something like:
while getopts a:b:c opt
do
case $opt in
a)
A_FLAG=$OPTARG
;;
b)
B_FLAG=$OPTARG
;;
c)
C_FLAG=1
;;
?)
usage
;;
esac
done
# discard all of our options.
shift `expr $OPTIND - 1`
if [ "$C_FLAG" = 1 ]; then
# Handle values as regular expressions
args=("$#")
C_LIST=()
for (( i=0 ; i <= $#-1 ; i++ ))
do
C_LIST=("${C_LIST[#]}" ${args[$i]})
done
fi
This script doesn't collect all the non-option arguments until after processing all the command line options.
Here's a question: why have a -c option at all?
If the full usage involves a list of values, why not just have no -c option and allow the -a and -b options only while the rest are regular args as in ./myscript.sh -a ARG_1 -b ARG_2 [argument ...], where any arguments are optional (like the -c option and its arguments are in your usage example?
Then your question becomes "how do I intersperse program options and arguments", to which I would respond: "You shouldn't do this, but to achieve this anyway, parse the command line yourself; getopts won't work the way you want it to otherwise."
Of course, parsing is the hard way. Another possibility involves adding the values after -c to a list, so long as you don't encounter another option or the end of the options:
C_LIST=()
while getopts a:b:c: opt; do
#Skipping code...
c)
C_LIST+="$OPTARG"
shift $(expr $OPTIND - 1)
while [ -n "$1" ] && [ $(printf "%s" "$1" | grep -- '^[^-]') ]; do
C_LIST+="$1"
shift
done
OPTIND=1
;;
The behaviour of getopts is mimicked: even if OPTARG begins with a '-' character, it is still kept, but after OPTARG, any string starting with the '-' character may simply be an invalid option such as -n. I used printf instead of echo because some versions of echo, such as the one that bash has built-in, have a -e option that may or may not allow the loop to continue, which isn't desired. The grep expression should prevent this, but who knows if that version of echo allows for -e'hello', which would cause grep to succeed because it sees "hello"? While possibly unnecessary, why take chances?
Personally, I'd avoid this behaviour if you can, but I also don't understand why you're asking for this behaviour in the first place. If I were to recommend anything, I'd suggest the more common /path/to/script -a ARG_1 -b ARG_2 [argument ...] style above any other possible choice of implementation.
On my system, I haven a /usr/share/doc/util-linux/examples/getopt-parse.bash file. It puts the result of getopt into a variable, and set the positional parameters to that variable. Then uses a switch similar to yours, but uses shift to remove arguments when found.
You could do something similar, but for your -c option use shift until you get an option or run out of arguments.
Or it might be enough for you to use your current solution, but remember to set the OPTIND variable after the loop.

How can I prevent an option that requires an argument to use the next option when no argument is given?

I have the following code in test.sh:
while getopts "f:i:" opt; do
case $opt in
f)
echo $OPTARG
i) echo $OPTARG
Now if I run ./test.sh -f I will get the error:
option requires an argument -- i
However, when I run ./test.sh -f -i test it will echo -i.
I know that this is because it just gets the next argument separated by a space, but is there an easy way to handle this?
I could do if [ $OPTARG == "-i" ]; then exit 1 but I'm hoping there is an easier way for when I have multiple options.
If you are using getopts, it has it's own ways. Just go with it.
After all, who says the option's argument cannot begin with a dash? If it's a filename, maybe the user wants the filename to begin with a dash. If it's a number, maybe it is a negative number.

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