cat file | head fails, when using "strict mode"

I use "strict mode" since several weeks. Up to now this was a positive experience.

But I do not understand this. It fails if I use `cat`.

```
#!/bin/bash

trap 'echo "ERROR: A command has failed. Exiting the noscript. Line was ($0:$LINENO): $(sed -n "${LINENO}p" "$0")"; exit 3' ERR
set -Eeuo pipefail

set -x
du -a /etc >/tmp/etc-files 2>/dev/null || true

ls -lh /tmp/etc-files

# works (without cat)
head -n 10 >/tmp/disk-usage-top-10.txt </tmp/etc-files

# fails (with cat)
cat /tmp/etc-files | head -n 10 >/tmp/disk-usage-top-10.txt

echo "done"
```

Can someone explain that?

> GNU bash, Version 5.2.26(1)-release (x86_64-pc-linux-gnu)

https://redd.it/1l8tjbx
@r_bash

Need Help Finding a Specific Config File in Linux

How to Find a Config File Created After 2020-03-03 (Size Between 25k and 28k)

I'm trying to track down a configuration file that meets these criteria:

Created/modified after March 3, 2020
Between 25KB and 28KB in size
Likely has a .conf or .cfg extension

I tried this command:

find / -type f \\( -name "\.conf" -o -name "*.cfg" \\) -size +25k -size -28k -newermt 2020-03-03 2>/dev/null

But I'm not sure if I'm missing anything. Some specific questions:

1. Are there other common locations besides /etc where configs might live?
2. Should I be using -cnewer instead of -newermt?
3. How would you modify this to also check file permissions?

https://redd.it/1l8zckm
@r_bash

Need Help: How to Check Services Listening on All Interfaces (IPv4 Only, Excluding Localhost)?

I’m auditing a system and need to find all services listening on all IPv4 interfaces (excluding localhost/127.0.0.1). Here’s what I’ve tried:



ss -tuln | grep -v "127.0.0.1" | awk '$5 !\~ /:::/ {print $5}' | cut -d: -f2 | sort -u



Questions:

1. Is this accurate?
2. Should I use netstat instead of ss for legacy systems?
3. How to also filter out IPv6 (:::) without complicating the command?

Context:

Target: Debian 12 server
Goal: Identify potentially exposed services (e.g., MySQL, Redis) bound to `0.0.0.0` or external IPs.

https://redd.it/1l92p9k
@r_bash

Bash noscript - How to check string length at specific loop iteration?

I'm working on a noscript that repeatedly base64 encodes a string, and I need to get the character count at a specific iteration. Here's what I have:

**#!/bin/bash**
**var="nef892na9s1p9asn2aJs71nIsm"**

**for counter in {1..40}**
**do**
**var=$(echo $var | base64)**
**# Need to check length when counter=35**
**done**

**What I need:**
When the loop hits iteration 35, I want to print ONLY the length of **$var** at that exact point.

**What I've tried:**

1. **${#var}** gives me length but I'm not sure where to put it
2. **wc -c** counts extra bytes I don't want
3. Adding **if \[ $counter -eq 35 \]; then echo ${#var}; fi**  but getting weird results

**Problem:**

* The length output disappears after more encodings
* Newlines might be affecting the count
* Need just the pure number as output

**Question:**
What's the cleanest way to:

1. Check when the loop is at its 35th pass
2. Get the exact character count of **$var** at that moment
3. Output just that number (no extra text or newlines)

https://redd.it/1latikt
@r_bash

curlmin - Curl Request Minimizer
https://github.com/noperator/curlmin

https://redd.it/1lahgv3
@r_bash

Built a Minimal TCP Port Scanner in C — Learning Networking from Scratch
https://www.reddit.com/gallery/1lbnqvt

https://redd.it/1lbnuss
@r_bash

Using cut to get versions

Suppose I have two different styles of version numbers:
- 3.5.2
- 2.45

What is the best way to use cut to support both of those. I'd like to pull these groups:

- 3
- 3.5

- 2
- 2.4

I saw that cut has a delemiter, but I don't see where it can be instructed to just ignore a character such as the period, and only count from the beginning, to however many characters back the two numbers are.

As I sit here messing with cut, I can get it to work for one style of version, but not the other.

https://redd.it/1lbtgyg
@r_bash

tzview - Display in local time lunchtime in other timezones.

I wrote a shell noscript that displays the current time in various
timezones. It is useful for organizing meetings with people in different
timezones, do not create a meeting at lunchtime to someone in Australia.

https://github.com/harkaitz/sh-tzview

https://redd.it/1ldj1fs
@r_bash

Rewriting a utility function noscripts library for Linux

I've made a simple utility functions noscripts librarytsilvs.bashlib for Bash.

Daily-driving Bazzite, I've designed it to simplify some interactions with Fedora Silverblue family of distros, especially rpm-ostree. But it might come in handy for active ADB and Git users too.

I'd like to reduce the amount of repetative code. If you have some time, review my code please. Re-implementation suggestions are welcome too.

tsilvs.bashlib: https://github.com/tsilvs/bashlib

https://redd.it/1ldnpge
@r_bash

Bash-based command-line tool to compare two folders and create html reports
https://redd.it/1le397d
@r_bash

nn - minimalist note taking tool for CLI using Zettelkasten in bash
https://github.com/joaocgduarte/nn

https://redd.it/1le09hz
@r_bash

Script to see how much space each incremental backup uses - may be useful

I've a noscript that uses rsync to create incremental backups, and I wanted have a list of the directories and the amount of space each backup is using. Here it is:

https://github.com/funkytwig/funkierbackup/blob/main/dir\_usage.bash

The output looks something like this:

/home/ben/test_backup/2025/06/15/23_D: 384KB
/home/ben/test_backup/2025/06/16/14_H: 128KB
/home/ben/test_backup/2025/06/16/15_H: 132KB
/home/ben/test_backup/2025/06/16/16_H: 120KB
/home/ben/test_backup/2025/06/16/17_H: 128KB
/home/ben/test_backup/2025/06/16/18_H: 120KB
/home/ben/test_backup/2025/06/16/19_H: 120KB
/home/ben/test_backup/2025/06/16/20_H: 120KB
/home/ben/test_backup/2025/06/16/21_H: 136KB
/home/ben/test_backup/2025/06/16/22_H: 128KB
/home/ben/test_backup/2025/06/16/23_D: 124KB
/home/ben/test_backup/2025/06/17/00_H: 120KB
/home/ben/test_backup/2025/06/17/01_H: 120KB
/home/ben/test_backup/2025/06/17/02_H: 120KB
/home/ben/test_backup/2025/06/17/03_H: 120KB
/home/ben/test_backup/2025/06/17/04_H: 120KB
/home/ben/test_backup/2025/06/17/05_H: 120KB
/home/ben/test_backup/2025/06/17/06_H: 120KB
/home/ben/test_backup/2025/06/17/07_H: 120KB
/home/ben/test_backup/2025/06/17/08_H: 120KB
/home/ben/test_backup/2025/06/17/09_H: 120KB
/home/ben/test_backup/2025/06/17/10_H: 120KB
/home/ben/test_backup/2025/06/17/11_H: 120KB
/home/ben/test_backup/2025/06/17/12_H: 120KB
/home/ben/test_backup/2025/06/17/13_H: 120KB
/home/ben/test_backup/2025/06/17/14_H: 184KB

https://redd.it/1ldns6p
@r_bash

Found a Bash-based uptime monitor… it’s just curl in a while loop

Discovered our “external uptime check” was literally -

while true; do
curl $SERVICE_URL
sleep 60
done

Running on a Raspberry Pi under someone’s desk, with no logging, no alerting, and no supervision.

Dropped it into Blackbox hoping for some clever logic. Nope. Just curl.

Anyone else stumbled across “creative” Bash in prod like this?

https://redd.it/1lejy8s
@r_bash

Go-like programming language that transpiles down to Batch or Bash

Hey Bash enthusiasts!

A while ago I wanted to get a bit into compiler/transpiler building and first I couldn't really think about something useful. So I thought, which language is super complicated to use even for the most basic tasks? And than it hit me...Batch! So that's what my small Go-like language became, a Batch transpiler, but it can also transpile to Bash (that's why I also posted it here).

Give it a try, I would like to hear your thoughts on it :)

https://github.com/monstermichl/TypeShell

https://redd.it/1lev9bi
@r_bash

I was reading this bash guide on GitHub ajd found this:
https://redd.it/1lf2hru
@r_bash

Help understanding ambiguous redirection behavior in bash

I'm working on building my own small shell that mimics bash behavior, and I'm trying to understand when and why "ambiguous redirect" errors happen.

Consider this situation:

export a=" " // just a bunch of spaces

Now these two examples behave differently:

ok$a"hhhhh"$.... // this is NOT ambiguous -works fine

ok$a"hhhhh"$USER // this IS ambiguous

I'm confused — why does using $a (which is just spaces) before a variable like $USER lead to an ambiguous redirect, but using it before a string of characters like ... doesn’t?

Also, I noticed that in some cases, $a splits the word:

ok$a"hhh"$USER # gets split due to spaces in $a

But in this case, it doesn’t seem to:

ok hhhhh$... # stays as one word?

Can someone explain when $a (or any variable with spaces) causes splitting, and how this leads to ambiguous redirection errors?

Thanks in advance!

https://redd.it/1lf6ccw
@r_bash

Terminal Commands That I Use to Boost Programming Speed
https://medium.com/gitconnected/terminal-commands-that-i-use-to-boost-programming-speed-e76b6ef07cb0?sk=84dc6150ea662198080fe12a1f4a0b81

https://redd.it/1lfx2m3
@r_bash

smart-pause-resume: An automation noscript designed for managing multiple media players on Linux efficiently.
https://github.com/erenseymen/smart-pause-resume

https://redd.it/1lg5dbw
@r_bash

how to make my bash code stop if the package manager is not valid?

https://preview.redd.it/nplcu96sng8f1.png?width=1920&format=png&auto=webp&s=00339818a850fa1992587e82186ca7269a4bf324



https://redd.it/1lhlbc2
@r_bash

Getting parent dir of file without path in one step in pure bash?

Is there an easy way to get the parent dir of a file without the path in pure bash? Or, in other words, get the substring of a variable between the last and next-to-last slash?

I know of

path='/path/to/pardir/file'
dirpath="${path%/}"
pardir="${dirpath##/}"
echo "$pardir"
pardir

With awk:

$ awk -F '/' '{sub(/\.^.+$/, "", $NF); print $(NF-1)}' <<< "$s"
$ pardir

and there's also expr match, although I'm not good with regexes. Not to mention dirname and basename.

Is there an easy, one-step incantation with pure bash so I can get this substring between the two last slashes?

https://redd.it/1li8ylt
@r_bash

50 GNU Commands X 50 PowerShell Commands
https://terminalroot.com/50-gnu-commands-x-50-powershell-commands/

https://redd.it/1lifp25
@r_bash