Creating a file using exec in Bash

Question

I am trying to use a shell program that I have been left to get running. The program starts as shown below.

#!/usr/bin/env bash
exec 3>&1 4>&2
trap 'exec 2>&4 1>&3' 0 1 2 3
exec 1>$1/logs/$(date '+%Y%m%d_%H%M%S')_start.log 2>&1

The program is a .sh with the input ($1) being the output folder such that it is looking in /output/logs..., the program fails on the exec line, this is my first time using bash and shell scripting but I think this line essentially redirects all the standard outputs to the log file?

The program error say

cannot create /output/logs/20230203_12345_start.log: directory non-existent

should this line also create the log file if it is non existent? I don't see how you could create the .log file first as otherwise you would get the seconds part of the title wrong?

As @Verpous pointed out the error message is about a missing directory, not a missing file, but to address "I don't see how you could create the .log file first as otherwise you would get the seconds part of the title wrong?" - if you did need to, you could create the file first by defining a variable to hold the file name, e.g. out="$1/logs/$(date '+%Y%m%d_%H%M%S')_start.log"; >"$out"; exec 1>"$out" 2>&1 — Ed Morton
– Ed Morton, Commented Feb 7, 2023 at 13:19

Verpous · Accepted Answer · 2023-02-07 12:13:23Z

4

It's not complaining about the file name, it says directory non-existent. I/O redirection can't make directories. Create it first with mkdir -p "$1"/logs, then your line should work.

answered Feb 7, 2023 at 12:13

Verpous

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1 Comment

Ed Morton Over a year ago

Always mkdir -p "$1"/logs || exit 1 or similar to make sure you did create the directory.

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