explain_popen(3)

💖 explain_popen — like, the whole manual page, bestie 💖

okay so this is explain_popen(3), and it lives in the Library Functions Manual section of your man pages. It's from libexplain, and it's literally here to tell you why your popen(3) call just flopped. no cap. 🫶

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🌸 NAME 🌸

explain_popen — explain popen(3) errors

like, the entire job of this thing is taking a popen(3) error and turning it into words you can actually read. iconic behaviour honestly. ✨

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🎀 SYNOPSIS 🎀

#include <libexplain/popen.h>
const char *explain_popen(const char *command, const char *flags);
const char *explain_errno_popen(int errnum, const char *command, const
char *flags);
void explain_message_popen(char *message, int message_size, const char
*command, const char *flags);
void explain_message_errno_popen(char *message, int message_size, int
errnum, const char *command, const char *flags);

four functions, one header, all the gossip. let's get into it. 💅

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🦋 DESCRIPTION 🦋

so these functions? you use them to get explanations for errors returned by the popen(3) system call. that's the whole vibe. 💜

✨ explain_popen ✨

const char *explain_popen(const char *command, const char *flags);

the explain_popen function is used to obtain an explanation of an error returned by the popen(3) system call. the least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail. like it's not gonna just say "something broke" and leave you on read. 💀

the errno global variable will be used to obtain the error value to be decoded.

this function is intended to be used in a fashion similar to the following example:

FILE *fp = popen(command, flags);
if (!fp)
{
    fprintf(stderr, "%s\n", explain_popen(command, flags));
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_popen_or_die(3) function. so if you're feeling lazy (no judgement, same) that one's already done for you. 🍓

• command — the original command, exactly as passed to the popen(3) system call.
• flags — the original flags, exactly as passed to the popen(3) system call.

Returns: the message explaining the error. this message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. this will be overwritten by the next call to any libexplain function which shares this buffer, including other threads. so don't go holding onto that pointer like it's your emotional support string, bestie 😭

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

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🌈 explain_errno_popen 🌈

const char *explain_errno_popen(int errnum, const char *command, const
char *flags);

the explain_errno_popen function is used to obtain an explanation of an error returned by the popen(3) system call. the least the message will contain is the value of strerror(errnum), but usually it will do much better, and indicate the underlying cause in more detail.

this function is intended to be used in a fashion similar to the following example:

FILE *fp = popen(command, flags);
if (!fp)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_popen(err, command, flags));
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_popen_or_die(3) function.

• errnum — the error value to be decoded, usually obtained from the errno global variable just before this function is called. this is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno. so grab it early or it's gone, fr fr. 🙈
• command — the original command, exactly as passed to the popen(3) system call.
• flags — the original flags, exactly as passed to the popen(3) system call.

Returns: the message explaining the error. this message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. this will be overwritten by the next call to any libexplain function which shares this buffer, including other threads.

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

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🧚 explain_message_popen 🧚

void explain_message_popen(char *message, int message_size, const char
*command, const char *flags);

the explain_message_popen function may be used to obtain an explanation of an error returned by the popen(3) system call. the least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail.

the errno global variable will be used to obtain the error value to be decoded.

this function is intended to be used in a fashion similar to the following example:

FILE *fp = popen(command, flags);
if (!fp)
{
    char message[3000];
    explain_message_popen(message, sizeof(message), command, flags);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_popen_or_die(3) function.

• message — the location in which to store the returned message. if a suitable message return buffer is supplied, this function is thread safe. 👑 that's the glow-up right there.
• message_size — the size in bytes of the location in which to store the returned message.
• command — the original command, exactly as passed to the popen(3) system call.
• flags — the original flags, exactly as passed to the popen(3) system call.

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⭐ explain_message_errno_popen ⭐

void explain_message_errno_popen(char *message, int message_size, int
errnum, const char *command, const char *flags);

the explain_message_errno_popen function may be used to obtain an explanation of an error returned by the popen(3) system call. the least the message will contain is the value of strerror(errnum), but usually it will do much better, and indicate the underlying cause in more detail.

this function is intended to be used in a fashion similar to the following example:

FILE *fp = popen(command, flags);
if (!fp)
{
    int err = errno;
    char message[3000];
    explain_message_errno_popen(message, sizeof(message),
        err, command, flags);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_popen_or_die(3) function.

• message — the location in which to store the returned message. if a suitable message return buffer is supplied, this function is thread safe.
• message_size — the size in bytes of the location in which to store the returned message.
• errnum — the error value to be decoded, usually obtained from the errno global variable just before this function is called. this is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.
• command — the original command, exactly as passed to the popen(3) system call.
• flags — the original flags, exactly as passed to the popen(3) system call.

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🔥 SEE ALSO 🔥

• popen(3) — process I/O
• explain_popen_or_die(3) — process I/O and report errors

like yeah go read those too, they're the supporting cast and they ate. 💅

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💜 COPYRIGHT 💜

libexplain version 1.4 Copyright (C) 2009 Peter Miller

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and that's the whole page, bestie!! 🎀✨ libexplain version 1.4, copyright (C) 2009 Peter Miller — go forth and let your error messages be verbose and beautiful. mwah. 💖🦋🌸 periodt.