Situation:

A non-root linux user owns a text file that's located in /etc, where the non-root linux user does not have permission to create files. The non-root linux user can edit the file manually via vi without issue. Programmatic and manual attempts to replace a text string within the file using 'sed -i', 'perl -i', and other in-directory temp file methods are failing due to permissions issues when the non-root linux user runs the text-replacement script. I've found a solution in the Perl Cookbook (noted farther down) but it has concerning warnings, plus it looks a bit beyond me at present. Can anyone suggest a simpler option?

Server Info:

cat /etc/os-release --> Oracle Linux Server 8.9

uname -a --> Linux server01.domain.com 5.4.17-2136.322.6.4.el8uek.x86_64

perl - (v5.26.3) built for x86_64-linux-thread-multi

sed - (GNU sed) 4.5

awk - GNU Awk 4.2.1, API: 2.0 (GNU MPFR 3.1.6-p2, GNU MP 6.1.2)

vi - VIM - Vi IMproved 8.0 (2016 Sep 12, compiled Aug 5 2022 07:42:15)

Location of file to edit:

/etc

Permissions on /etc:

drwxr-xr-x 130 root root 12288 Jun 21 11:50 etc

Text file to edit:

/etc/targetfile -rw-rw-r-- 1 justauser group1 1864 Jun 19 10:52 targetfile

File length of /etc/targetfile can be as large as 200 lines that are about 50 characters each.

Example/abbreviated /etc/targetfile contents:

f1112:/dir1/dir2/59.35:N # Comment f3332:/dir1/dir2/59.35:N # Comment f4442:/dir1/dir2/59.35:N # Comment f555:/dir1/dir2/59.35:N # Comment f666s2:/dir1/dir2/59.35:N # Comment f777s2:/dir1/dir2/59.35:N # Comment 

Goal: Programmatically change /dir1/dir2/59.35 to /dir1/dir2/59.77 in targetfile located in /etc, where the non-root user running the script is "justauser" who lacks permissions to create files in /etc.

Constraints:

-Permissions on /etc can't change.

-Existing server programs/utilities can't be upgraded.

-All programs/commands must be called from within a bash shell script.

-The bash shell script must be executed as "justauser", not as root.

-Not using sudo is strongly preferred.

Miscellaneous:

While logged in as the linux user "justauser", command line editing /etc/targetfile using vi works fine. Commands like 'sed -i' and 'perl -i' fail since "justauser" lacks write perms in /etc to create temp files.

perl -i -p -e 's/f4442:\/dir1\/dir2\/59.35:N/f4442:\/dir1\/dir2\/59.77:N/g' /etc/targetfile --Can't remove /etc/targetfile: Permission denied, skipping file. sed -i 's/f4442:\/dir1\/dir2\/59.35:N/f4442:\/dir1\/dir2\/59.77:N/' /etc/targetfile --sed: sed: couldn't open temporary file /etc/sedO2SLSF: Permission denied 

Rough Intended Usage Example (static values replacing variables to come): #!/bin/bash ... function _editConfig { echo "Editing targetfile..." perl -i -p -e 's/f4442:\/dir1\/dir2\/59.35:N/f4442:\/dir1\/dir2\/59.77:N/g' /etc/targetfile if [ $? -ne 0 ] then echo "Error on _editConfig function.\n Terminating program" EXITCODE=1 fi } ... 

Options seen:

Perl Cookbook 7.10 Modifying a File in Place Without a Temporary File:

open(F, "+< $infile") or die "can't read $infile: $!"; $out = ''; while (<F>) { s/DATE/localtime/eg; $out .= $_; } seek(F, 0, 0) or die "can't seek to start of $infile: $!"; print F $out or die "can't print to $infile: $!"; truncate(F, tell(F)) or die "can't truncate $infile: $!"; close(F) or die "can't close $infile: $!"; ... "This approach is for the truly determined. It's harder to write, takes more memory (potentially a lot more), doesn't keep a backup file, and may confuse other processes trying to read from the file you're updating. For most purposes, therefore, we suggest it's probably not worth it." 

Final Comments:

Is there an in-place edit option that doesn't use an in-directory temp file that is simpler than the Perl Cookbook example?

The Perl Cookbook example is a bit hard to follow for a Perl novice, and it also requires some kind of modification/conversion... I'd think...to work in the body of the bash script.