File & Misc Commands Cheat Sheet (Compare, Search, Archive, Hash, Convert)

Essential Linux file commands for comparing, deleting securely, timestamps, disks/mounts, checksums, searching text/files, archiving/compressing, splitting/carving with dd, conversions, attributes, and useful misc ops like disabling history, compiling, rebooting, and URL extraction.

Compare / diff

```
diff file file2
```
Compare two text files line-by-line and show differences.

Delete / secure delete

```
rm -rf dir
```
Force delete a directory recursively (dangerous: no prompt, removes everything under dir).
```
shred -f -u file
```
Overwrites file contents to make recovery harder, then removes it (-u). -f forces permissions if possible.

Timestamps

```
touch -r ref_file file
```
Sets file timestamps (atime/mtime) to match ref_file.
```
touch -t YYYYMMDDHHMM.SS file
```
Sets timestamp explicitly (note the correct format includes minutes and optional .SS).
Example:
```
touch -t 202601301530.00 notes.txt
```

Disks / partitions / mounting

```
sudo fdisk -l
```
Lists disks and partitions (connected drives). (-l is “list”; not -1.)
```
sudo mount /dev/sda# /mnt/usbkey
```
Mounts a partition to a directory (replace # with partition number, e.g., /dev/sda1).
Example:
```
sudo mount /dev/sda1 /mnt/usbkey
```

Hashing / checksums

```
md5sum -t file
```
Computes MD5 checksum. (-t is “text mode”; often unnecessary on Linux.)
```
echo -n "str" | md5sum
```
Generates an MD5 hash of a string (-n avoids adding a newline).
```
sha1sum file
```
Computes SHA1 checksum. (Your shalsum corrected to sha1sum.)

Sorting / unique lines

```
sort -u
```
Sorts input and outputs unique lines (removes duplicates).
Example:
```
sort -u list.txt
```

Grep searching

```
grep -c 'str' file
```
Counts matching lines containing str in file.
```
grep -Hnri word * | vim -
```
Recursively searches for word in files under the current directory:
- -H show filename, -n line number, -r recursive, -i ignore case
  Pipes results into vim for viewing (vim - reads stdin).
```
grep -rial word .
```
Recursively lists filenames that contain word:
- -r recursive, -i ignore case, -a treat binary as text, -l only names.

Tar archives (create/extract)

```
tar cf file.tar files
```
Creates a .tar archive from files.
```
tar xf file.tar
```
Extracts a .tar archive.
```
tar czf file.tar.gz files
```
Creates a gzip-compressed tarball.
```
tar xzf file.tar.gz
```
Extracts a gzip-compressed tarball.
```
tar cjf file.tar.bz2 files
```
Creates a bzip2-compressed tarball.
```
tar xjf file.tar.bz2
```
Extracts a bzip2-compressed tarball.

gzip compression

```
gzip file
```
Compresses file into file.gz (original removed by default).
```
gzip -d file.gz
```
Decompresses file.gz back to file. (file. gz corrected to file.gz.)

UPX packer

```
upx -9 -o out.exe orig.exe
```
Compresses/“packs” an executable with maximum compression (-9) outputting out.exe.

Zip

```
zip -r zipname.zip Directory/
```
Creates a zip archive recursively from a directory.

dd (extract/carve a portion of a file)

```
dd skip=1000 count=2000 bs=5 if=infile of=outfile
```
Copies a slice of data from infile to outfile:
- skips 1000 blocks, then copies 2000 blocks, block size 5 bytes
  Total extracted bytes = count * bs (here 10,000 bytes).

split (chunk files)

```
split -b 9K file prefix
```
Splits file into 9 KB chunks named prefixaa, prefixab, etc.

Line ending conversion / text cleanup

```
awk '{ sub("\r$", ""); print }' unix.txt > win.txt
```
Removes Windows CR (\r) at end-of-line, producing Unix-style output.
(Your awk expression corrected and made functional.)
```
dos2unix file
```
Converts DOS/Windows line endings (CRLF) to Unix (LF).

find (files, PDFs, permissions)

```
find / -iname '*.pdf'
```
Searches case-insensitively for PDF files across /.
```
find / $ -perm -4000 -o -perm -2000 $ -type f -exec ls -ldb {} \;
```
Finds setuid (4000) or setgid (2000) files and lists them in detailed form.

File type / metadata

```
file file
```
Detects file type (text, ELF executable, PDF, image, etc.).

File attributes (immutable bit)

```
chattr +i file
```
Makes a file immutable (cannot be modified/deleted even by root until removed).
```
chattr -i file
```
Removes immutable attribute.

Infinite nested directory traversal

```
while [ $? -eq 0 ]; do cd flag/; done
```
Keeps changing into flag/ repeatedly while the previous cd succeeded; useful when directories are nested the same way.

Miscellaneous commands

```
unset HISTFILE
```
Disables writing shell history to the history file for the current session (does not erase existing history).
```
ssh user@ip "arecord -f cd -t raw" | aplay
```
Records audio from the remote machine’s default microphone (arecord) and plays it locally (aplay).
(Your original line corrected to a working form; audio devices and permissions must exist.)
```
gcc -o outfile myfile.c
```
Compiles a C program (myfile.c) into an executable named outfile. (For C++ typically use g++.)
```
init 6
```
Reboots the machine (runlevel 6). (init 0 = shutdown). On systemd systems, prefer reboot/shutdown.
```
cat /etc/syslog.conf | grep -v '#'
```
Prints non-comment lines from syslog config.
(Your path/pipe corrected; on many Linux systems syslog config may be /etc/rsyslog.conf.)
```
grep 'href=' file | cut -d'/' -f3 | grep url.com | sort -u
```
Extracts hostnames from lines containing href= by splitting on /, filters for url.com, outputs unique sorted results. (Basic parsing; HTML can be messy.)
```
dd if=/dev/urandom of=file bs=3145728 count=100
```
Generates a random file: 3,145,728 bytes per block (~3 MiB) × 100 ≈ 300 MiB total.

Important additions for this topic

Safer deletion / prompts / trash

```
rm -ri dir
```
Interactive recursive delete (asks before removing).

Quick directory sizing / space usage

```
du -sh *
```
Shows size of each item in current directory.

Faster searching / indexing

```
locate filename
```
Fast filename search (uses a database; may require updatedb).

Copy / move / permissions

```
cp -a source dest
```
Archive copy (preserves permissions, timestamps, symlinks).
```
rsync -avP source/ dest/
```
Reliable copy with progress and resume behavior.

Inspect archives without extracting

```
tar tf file.tar.gz
```
Lists contents of a tarball.

aw-junaid/files.md

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