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Use Long Options in Scripts

matklad.github.io

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Re: Use Long Options in Scripts

#151

Post by account42 »

bonoboTP wrote: post #82
ezequiel-garzon wrote: post #69

Earlier quoted context omitted.

It does if single or double quotes are used, right? Which would be necessary (or preferred to multiple backslashes) quite often.

No, the quotes are not seen by the program. The program receives a list of strings, it does not get the information about whether and how those strings were originally quoted in the shell. Programs can also be directly called with lists of strings as in execve, so often it does not even make sense to ask if the arguments were quoted or not. Quotes live on a different level of abstraction.

Note that this is true for POSIX sytems but not e.g. for Windows. There the program receives the command-line as-is and is responsible for parsing it into an array. There are two different standard functions to do this parsing for you (with slightly different quoting behavior) but you could also create your own that requires options to not be quoted.

Re: Use Long Options in Scripts

#152

Post by account42 »

bluedino wrote: post #85
arcanemachiner wrote: post #35

Earlier quoted context omitted.

I know to do this intuitively, but I have no idea why.

It's worth it just to watch the frustration of a junior when they try tacking more arguments on the end of a command.

A great opportunity to teach the importance of reading the whole command before trying to modify it.

Re: Use Long Options in Scripts

#153

Post by account42 »

amelius wrote: post #88

Before invoking a command, always first check if the length of the command is not longer than ARG_MAX. For example, if this is your command: grep --ignore-case --files-with-matches -- "hello" *.c Then invoke it as follows: CMD="grep --ignore-case --files-with-matches -- \"hello\" *.c" ARG_MAX=$(getconf ARG_MAX) CMD_LEN=${#CMD} if (( CMD_LEN > ARG_MAX )); then echo "Error: Command length ($CMD_LEN) exceeds ARG_MAX ($A…

If you are doing something where going over ARG_MAX is a real possibility it would be better to write your scripts to avoid the problem altogether rather than awkwardly try to detect it wit ha bonus exploit. For example, many commands can accept a list of files on standard input or from a list file.

Re: Use Long Options in Scripts

#154

Post by bonoboTP »

danadam wrote: post #93
bonoboTP wrote: post #82

Earlier quoted context omitted.

No, the quotes are not seen by the program. The program receives a list of strings, it does not get the information about whether and how those strings were originally quoted in the shell. Programs can also be directly called with lists of strings as in execve, so often it does not even make sense to ask if the arguments were quoted or not. Quotes live on a different level of abstraction.

> No, the quotes are not seen by the program. The program receives a list of strings, it does not get the information about whether and how those strings were originally quoted in the shell. With quotes the program will receive a single argument -n␣o␣p␣e instead of multiple ones -n, o, p, e. At least it works on the machine here: ]$ echo "-n o p e" -n o p e ]$ /bin/echo "-n o p e" -n o p e

Yes, I think there was some misremembering here. The nontrivial thing is to print out -n itself with echo. For example, echo doesn't treat "--" specially, so "echo -- -n" prints "-- -n".

Re: Use Long Options in Scripts

#155

Post by hulitu »

mceachen wrote: post #118
Wowfunhappy wrote: post #87

Earlier quoted context omitted.

> However, while writing programs that need to invoke POSIX commands in a portable manner ...probably a stupid question, but something I have earnestly been wondering about... when does this actually happen nowadays? What POSIX systems are you targeting that aren't one of the major ones (Linux, Darwin, or one of the major BSDs)? I was writing a shell script a few months ago that I wanted to be very durable, and I tar…

Alpine docker images only come with dash instead of bash, which _may_ run your sh script, but test thoroughly. Or just install bash. FWIW, Darwin/macOS is especially guilty of gobsmackingly ancient coreutils that don’t support long option variants.

P in POSIX stands for portability. ,/s

Re: Use Long Options in Scripts

#156

Post by hulitu »

amelius wrote: post #88

Before invoking a command, always first check if the length of the command is not longer than ARG_MAX. For example, if this is your command: grep --ignore-case --files-with-matches -- "hello" *.c Then invoke it as follows: CMD="grep --ignore-case --files-with-matches -- \"hello\" *.c" ARG_MAX=$(getconf ARG_MAX) CMD_LEN=${#CMD} if (( CMD_LEN > ARG_MAX )); then echo "Error: Command length ($CMD_LEN) exceeds ARG_MAX ($A…

> Before invoking a command, always first check if the length of the command is not longer than ARG_MAX.

Tell that to Google and Mozilla. /s

Re: Use Long Options in Scripts

#157

Post by pingiun »

mceachen wrote: post #118
Wowfunhappy wrote: post #87

Earlier quoted context omitted.

> However, while writing programs that need to invoke POSIX commands in a portable manner ...probably a stupid question, but something I have earnestly been wondering about... when does this actually happen nowadays? What POSIX systems are you targeting that aren't one of the major ones (Linux, Darwin, or one of the major BSDs)? I was writing a shell script a few months ago that I wanted to be very durable, and I tar…

Alpine docker images only come with dash instead of bash, which _may_ run your sh script, but test thoroughly. Or just install bash. FWIW, Darwin/macOS is especially guilty of gobsmackingly ancient coreutils that don’t support long option variants.

the alpine default shell is called "ash", "dash" is the debian/ubuntu default shell
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