diff --git a/knowledge base/get the current shell.md b/knowledge base/get the current shell.md
new file mode 100644
index 0000000..a5bec75
--- /dev/null
+++ b/knowledge base/get the current shell.md	
@@ -0,0 +1,40 @@
+# Get the current shell
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+   1. [Sources](#sources)
+
+## TL;DR
+
+```sh
+# Full path of the current shell's executable with arguments.
+ps -o 'command='
+
+# Full path of the current shell's executable only.
+ps -o 'comm='
+
+# Only the executable name.
+ps -co 'comm='
+
+# Unreliable: if the SHELL variable is set by a previous shell, that one is the
+# value that will be shown.
+echo "$SHELL"
+echo "$0"
+```
+
+## Further readings
+
+### Sources
+
+- [Remove the first line of a text file in Linux]
+
+<!--
+  References
+  -->
+
+<!-- In-article sections -->
+<!-- Knowledge base -->
+<!-- Files -->
+<!-- Upstream -->
+<!-- Others -->
+[remove the first line of a text file in linux]: https://www.baeldung.com/linux/remove-first-line-text-file
diff --git a/knowledge base/grep.md b/knowledge base/grep.md
index 12d07e4..8562fc5 100644
--- a/knowledge base/grep.md	
+++ b/knowledge base/grep.md	
@@ -23,6 +23,9 @@ grep -R --exclude-dir 'excluded/dir' 'pattern' 'path/to/search/recursively'   #
 # Show line numbers.
 grep -n 'pattern' 'path/to/search'
 
+# Only print the part matching the pattern.
+ps | grep -o '/.*/fish' | head -n '1'
+
 # Multiple parallel searches.
 # Mind files with spaces in their name.
 find . -type f | parallel -j +100% grep 'pattern'
@@ -34,15 +37,15 @@ grep --color '[[:digit:]]' 'file.txt'
 
 ## Variants
 
-- [`egrep`](#egrep) to use regular expressions in search patterns, same as `grep -E`
-- [`fgrep`](#fgrep) to use patterns as fixed strings, same as `grep -F`
+- `egrep` to use regular expressions in search patterns, same as `grep -E`
+- `fgrep`] to use patterns as fixed strings, same as `grep -F`
 - [archive-related variants](#archive-related-variants) for searching into compressed files
 - [`pdfgrep`](#pdfgrep) for searching into PDF files
 
 ### Archive-related variants
 
-- [`xzgrep`](#xzgrep) (with `xzegrep` and `xzfgrep`)
-- [`zstdgrep`](#zstdgrep) for zstd archives
+- `xzgrep` (with `xzegrep` and `xzfgrep`)
+- `zstdgrep` for zstd archives
 - many many others
 
 ### PDFgrep