@@ Fedora AWK/Pipe Corruption Bug Report :2025-11-30_Sun:LxtAnx9c:  op{
# Fedora Bug Report: gawk/Pipe Corruption (Fedora 42)

1. TITLE (One-Line Summary)

Regression: Bash command substitution (`$()`) running `gawk` permanently corrupts shell file descriptors (FD 0/1), even with explicit `< /dev/null` redirection.


2. ENVIRONMENT DETAILS

• OS: Fedora 42 (x86_64)
• Kernel: `6.17.8-200.fc42.x86_64`
• Package: `gawk-5.3.1-1.fc42.x86_64`
• Shell: `bash` (version 5.2 or similar)

• Behavior: When `gawk` is executed in a command substitution (`$()`), the parent shell's I/O streams are permanently linked (`stdin` == `stdout`), causing safety checks in other programs like `cat` to fail.


3. STEPS TO REPRODUCE

	1. Start a fresh interactive terminal session.

	2. Create a simple configuration file: ```bash $ echo "key value" > test.cfg ```

	3. Run the command substitution using `awk`, explicitly redirecting its Standard Input (FD 0) to `/dev/null`: ```bash $ test_var=$(awk '/^key / {print $2}' test.cfg < /dev/null) ```

	4. Immediately try to run the standard, interactive `cat` command: ```bash $ cat ```

4. ACTUAL RESULTS

The `cat` command fails with the I/O safety error:


``` cat: -: input file is output file ```

5. EXPECTED RESULTS

The command substitution should run silently, and the `cat` command should wait for keyboard input (the standard interactive behavior).

6. CRITICAL DIAGNOSTIC INFORMATION

The bug is not an `awk` default behavior issue. The corruption occurs despite the explicit redirection of FD 0 using `< /dev/null`. This implies a deeper issue in how the Bash pipe mechanism interacts with the `gawk` executable in this specific Fedora environment.


A functionally similar command using `sed` does NOT cause the error, even when run inside the same command substitution:


```bash $ test_var=$(sed -n '/^key /p;q' test.cfg) $ cat  # This works fine and does not trigger the error. ```


This suggests an internal conflict within the `gawk` binary itself or how the operating system handles the file descriptors when `gawk` is initialized inside a pipeline. The bug is a regression because this behavior did not occur in previous Fedora versions.


Reproducible: Always

Steps to Reproduce:


3. STEPS TO REPRODUCE

	1. Start a fresh interactive terminal session.

	2. Create a simple configuration file: ```bash $ echo "key value" > test.cfg ```

	3. Run the command substitution using `awk`, explicitly redirecting its Standard Input (FD 0) to `/dev/null`: ```bash $ test_var=$(awk '/^key / {print $2}' test.cfg < /dev/null) ```

	4. Immediately try to run the standard, interactive `cat` command: ```bash $ cat ```

4. ACTUAL RESULTS

The `cat` command fails with the I/O safety error:


``` cat: -: input file is output file ```

5. EXPECTED RESULTS

The command substitution should run silently, and the `cat` command should wait for keyboard input (the standard interactive behavior).

6. CRITICAL DIAGNOSTIC INFORMATION

The bug is not an `awk` default behavior issue. The corruption occurs despite the explicit redirection of FD 0 using `< /dev/null`. This implies a deeper issue in how the Bash pipe mechanism interacts with the `gawk` executable in this specific Fedora environment.


A functionally similar command using `sed` does NOT cause the error, even when run inside the same command substitution:
3. STEPS TO REPRODUCE

	1. Start a fresh interactive terminal session.

	2. Create a simple configuration file: ```bash $ echo "key value" > test.cfg ```

	3. Run the command substitution using `awk`, explicitly redirecting its Standard Input (FD 0) to `/dev/null`: ```bash $ test_var=$(awk '/^key / {print $2}' test.cfg < /dev/null) ```

	4. Immediately try to run the standard, interactive `cat` command: ```bash $ cat ```

4. ACTUAL RESULTS

The `cat` command fails with the I/O safety error:


``` cat: -: input file is output file ```

5. EXPECTED RESULTS

The command substitution should run silently, and the `cat` command should wait for keyboard input (the standard interactive behavior).

6. CRITICAL DIAGNOSTIC INFORMATION

The bug is not an `awk` default behavior issue. The corruption occurs despite the explicit redirection of FD 0 using `< /dev/null`. This implies a deeper issue in how the Bash pipe mechanism interacts with the `gawk` executable in this specific Fedora environment.


A functionally similar command using `sed` does NOT cause the error, even when run inside the same command substitution: