> For the complete documentation index, see [llms.txt](https://www.shellspells.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.shellspells.net/linux/file-ops/modify-content.md). # Modify Content Note: `sed -i` will change original file. ## Overwrite

Command	Description
`cat > file`	Overwrite/create file
`echo "text" > [file]`	Overwrite/create file
`echo "text" \| tee [file]`	Overwrite/create file and display
`printf "Line 1\nLine 2" > [file]`	Overwrite/create file with newlines.
`awk -v text="some text" 'BEGIN{print text > "filename"}'`	Overwrite/create file
`echo "text" \| dd of=file`	Write "text" to `file` using `dd`, overwriting existing contents.

## Insert ### Strings

Command	Description
`echo "text" >> [file]`	Append "text" to the end of a file.
`sed i\text`	Before each line
`sed a\text`	After each line
`sed '$ a\text' [file]`	Use `sed` to insert "text" at the end of a file.
`sed '$a text' file`	Append "text" at the end of `file`.
`sed '1i text' file`	Insert "text" at the beginning of `file`
`awk 'END {print "text"} 1' file > temp && mv temp [file]`	Append "text" at the end of a file.

### Lines

Command	Description
`sed '1i\New line' [file]`	Insert newline at beginning
`sed '$a\New line' [file]`	Append new line at the end
`sed '/pattern/a\new line' file`	Append new line after lines with pattern
`sed G [file]`	Adds blank line between lines (Double Space)
`nl -ba file > temp && mv temp file`	Add line numbers to each line.
`awk '{print NR, $0}' file > temp && mv temp file`	Add line numbers to each line.

### Append

Command	Description
`cat >> file`	Append to `file` from stdin until EOF (Ctrl+D).
`echo "text" \| tee -a [file]`	Append and display
`printf "text" >> [file]`	Append
`awk -v text="more text" '{print $0 ORS text}' [file]`	Append?

## Replace / Remove ### Replace Strings

Command	Description
`sed 's/pattern/new/' [file]`	Replace pattern with new in file.txt
`sed 's/pattern/new/g' [file]`	Replace all occurrences of "old" with "new".
`sed 's/pattern/new/2' [file]`	Replace 2nd pattern in a line.
`sed '2 s/pattern/new/' [file]`	Replace pattern on line 2
`sed 1,5s/pattern/new/ [file]`	Replace pattern on lines 1 to 5
`sed /pattern/, /pattern2/s/old/new/`	Replace between two patterns
`sed $s/pattern/new/`	Replace pattern on last line
`sed 's/,/\n/g' file`	Replace Commas with Newline
`tr , '\n' < file`	Replace Commas with Newline

Replaces occurrences of 'old\_pattern' with 'new\_pattern' and prints each line: ```bash awk '{gsub(/old_pattern/, "new_pattern"); print}' [file] ``` Globally replace "old" with "new" in a file. ```bash awk '{gsub(/old/, "new"); print}' [file] > temp && mv temp [file] ``` Finds and replaces text within a specified range: ```bash awk '/start_pattern/, /end_pattern/ {gsub(/old_pattern/, "new_pattern"); print}' [file] ``` Use `perl` to replace "old" with "new" in a file, similar to `sed`: ```bash perl -pi -e 's/old/new/g' [file] ``` ### Remove Strings | Command | Description | | ------------------------------------------------------------- | ------------------------------------ | | `cut -f 1 -d $'\t' [file]` | Suppressing Non-Printable Characters | ### Remove Lines #### Patterns

Command	Description
`sed '/pattern/d' file`	Remove lines matching "pattern".
`awk '!/pattern/' file > temp && mv temp file`	Remove lines matching "pattern".
`grep -v "pattern" file > temp && mv temp file`	Use `grep` with `-v` to filter out lines matching "pattern".

#### Line Numbers | Command | Description | | ------------------------------------------------------- | ---------------------------- | | `sed '/^9/d' [file]` | Delete lines starting with 9 | | `sed '1,3d' [file]` | Delete lines 1 to 3 | #### Blank Lines

Command	Description
`sed '/^$/d' [file]`	Remove blank lines.
`sed 'n;d'`	Remove blank lines between lines (Double Spaced) (assumes even numbered lines are blank)
`awk 'NF' [file] > temp && mv temp [file]`	Remove blank lines, keeping lines with at least one field.

#### Duplicate Lines

Command	Description
`awk '!seen[$0]++' file > temp && mv temp file`	Remove duplicate lines, preserving the order.
`sort -u file > temp && mv temp file`	Sort the file and remove duplicate lines, may change the original order.

#### Comment Lines Removing lines that start with `#`. E ssentially this removes all the comments out of a file. This is good when examining a config file full of comments when you just want to see a certain line. ```bash cat | grep -v ^\# | grep . ``` ```bash sed '/^#/d' ``` ## Convert Case

Command	Description
`tr '[:upper:]' '[:lower:]' < file > temp && mv temp file`	Convert all text to lowercase.
`tr '[:lower:]' '[:upper:]' < file > temp && mv temp file`	Convert all text to uppercase.
`awk '{print tolower($0)}' file > temp && mv temp file`	Convert all text to lowercase using `awk`.
`awk '{print toupper($0)}' file > temp && mv temp file`	Convert all text to uppercase using `awk`.

## Text Editors

Command	Description
`vim file`	Open `file` in Vim editor for editing. Save and exit with `:wq`.
`nano file`	Open `file` in Nano editor for editing. Save and exit with `Ctrl+O`, `Ctrl+X`.
`emacs file`	Open `file` in Emacs editor for editing. Save with `Ctrl+x Ctrl+s` and exit with `Ctrl+x Ctrl+c`.