CODEWITHSUNDEEP
bashscriptingstderr
lazereyes
lazereyes

Reputation: 107

stderr redirection is causing read command to not print output

A code as

#!/bin/bash

exec 3>&1 4>&2
exec 1>/tmp/stdout.log
exec 2>/tmp/stderr.log
PS4='+ (Line $LINENO) '
set -x
echo "This goes to /tmp/stdout.log"
echo "This goes to /tmp/stderr.log" 1>&2
cmd1="$(uname -a)"
cmd2="$(uname +-a)"

exec 1>&3
read -n 1 -s -r -p "Please do manually Installation of package ,Press any key to continue"



exec 1>&3 2>&4
exec 3>&- 4>&-

I tried to restore exec 1>&3 so read is echo but its not showing when i do normal echo "hello" it shows but not with read.

For selective places in code where I want to user intervention I restore output handling but instead the script waits for command to enter and then execute.

Upvotes: 1

Views: 56

Answers (1)

Mike Holt
Mike Holt

Reputation: 4602

You are expecting read to print to stdout, but it prints to stderr as demonstrated by this command:

> read -p "prompt" 2>/dev/null # this command will print nothing

Look in your /tmp/stderr.log. The missing prompt will be in there.

To restore the ability of read to print to your screen, instead of restoring stdout, you need to restore stderr:

exec 2>&4
read -n 1 -s -r -p "Please do manually Installation of package ,Press any key to continue"

Alternatively, as noted in the comments, instead of restoring stderr with a separate command, you can restore it just for the read command:

read -n 1 -s -r -p "<shortened for clarity>" 2>&4

Upvotes: 2

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