
## `grep`

### Basics

```shell
grep [options] <pattern> <file> # Basic usage
grep "spam" <file> # Search for lines that contain `spam` in file
grep -v "spam" <file> # Search for lines that do _not_ contain `spam` in file
grep -i "spam" <file> # Case-insentive search
grep -n "spam" <file> # Print line numbers
grep -nr 'string*' . # Recursively search current directory for `string`
```

### Regular expressions

See also: <Link href="/notes/regex">/notes/regex</Link>

```shell
grep "^eggs" <file> # Find all lines starting with `eggs`
grep "eggs$" <file> # Lines ending with `eggs`
grep "^[A-Z]" <file> # Lines beginning with an uppercase letter
grep "^[[:upper:]]" <file> # Equivalent to above; Using POSIX classes
```

### Extended regular expressions

Along with basic regular expressions (BREs, which is the default), `grep` also supports [extended regular expressions (EREs)](https://en.wikipedia.org/wiki/Regular_expression#Standards) by using the `-E` option or by calling the `egrep` command.

```shell
grep "$group$" <file> # Grouping
grep -E "(group)" <file> # Equivalent to above
grep -E "(GPL|General Public License)" <file> # Alternation
grep -E "(copy)?right" <file> # Quantification; Match `copy` zero or one time
grep -E "free[^[:space:]]+" <file> # Match the string `free` plus one or more characters that are not white space characters
grep -E "[AEIOUaeiou]{3}" <file> # Match lines that contain triple-vowels
grep -E "[[:alpha:]]{16,20}" <file> # Match any words that have between 16 and 20 characters
```

### Miscellaneous

```shell
grep . * # cat a bunch of files
```

- Find lines in one file that are not in another [[\*](https://stackoverflow.com/questions/18204904/fast-way-of-finding-lines-in-one-file-that-are-not-in-another)]

  ```shell
  grep -v -f file1 file2
  ```

## `ripgrep`

```shell
rg -S 'string' # Case-insentive search
```


g/re/p

[Top]

`grep`

Basics

Regular expressions

Extended regular expressions

Miscellaneous

`ripgrep`


## Basics

```shell
git config # Set user-specific configuration values like email, username, editor, etc
git clone # Clone a repository into a new directory
git init # Create an empty Git repository

git add # Add files for staging
git rm # Remove files from the working tree and from the index
git status # Show changes staged for next commit
git diff # Show changes between commits, commit and working tree, etc
git show # Show information about any git object
git log # Show commit logs
git bisect # Use binary search to find the commit that introduced a bug

git commit # Record changes to the repository
git branch # List, create, or delete branches
git checkout # Switch to another branch
git merge # Join two or more branches together
git rebase # Reapply commits on top of another base tip
git reset # Reset current HEAD to the specified state
git stash # Stash the changes in a dirty working directory away
git tag # Create, list, delete or verify a tag object signed with GPG

git remote # View all remote
git fetch # Fetch all objects from the remote repository that don’t currently reside in the local working directory
git pull # Merge all the changes present in the remote repository to the local working directory
git push # Update remote with committed changes
```

## Useful options

```shell
git log --oneline # Display single commit information per line
git rev-list HEAD --count # Total number of commits
git shortlog # Summarize `git log` output
git commit --amend -m "New commit message" # Edit the last commit message
```

## Miscellaneous

- Remove a file from history

  ```shell
  git filter-branch --force --index-filter \
    "git rm --cached --ignore-unmatch PATH-TO-YOUR-FILE-WITH-SENSITIVE-DATA" \
    --prune-empty --tag-name-filter cat -- --all
  ```

- Get a list of the deleted files in history

  ```shell
  ## without commit hashes
  git log --diff-filter=D --summary | grep delete

  ## with commit hashes
  git log --diff-filter=D --summary | grep -E 'delete|^commit\s+\S+'
  ```

- Amend older or multiple commit messages

  - Display a list of the last n commits in the default text editor:

    ```shell
    git rebase -i HEAD~n
    ```

  - Replace `pick` with `reword` before each commit message you want to change, save and close the commit list file.
  - In each resulting commit file, type the new commit message, save the file, and close it.
  - Push the amended commits:

    ```shell
    git push --force
    ```

- Amend the very first commit message [[\*](https://stackoverflow.com/a/14630424)]

  ```shell
  git rebase -i --root
  ```

- Squash all previous commits into one [[\*](https://stackoverflow.com/a/23486788)]

  ```shell
  git reset $(git commit-tree HEAD^{tree} -m "A new start")
  ```

- See the diff for a commit [[\*](https://stackoverflow.com/a/17563864)]

  ```shell
  git show <commit> # or one of these
  git show --color --pretty=format:%b <commit>
  git diff-tree -p <commit>
  ```

- Print a leaderboard of authors based on number of commits in a repository

  ```shell
  git log --format='%aN' | sort | uniq -c | sort -nr
  git log --format='%aN' | sort -u # Print all contributors in alphabetical order
  ```

- Working with multiple GitHub accounts with SSH [[\*](https://code.tutsplus.com/tutorials/quick-tip-how-to-work-with-github-and-multiple-accounts--net-22574)]

  - [Create a new SSH key](./ssh) and add it to GitHub account #2. Save the private key file as something like `id_rsa_2`.

  - Update the SSH config:

    ```shell title=".ssh/config"
    # Default GitHub
    Host github.com
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_rsa

    # GitHub account #2
    Host github-alt
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_rsa_2
    ```

  - When pushing to GitHub account #2, change the remote to reflect the new host:

    ```shell
    # git remote add origin git@github.com:username/repository.git
    git remote add origin git@github-alt:username/repository.git
    git push origin main
    ```



```shell
sed [options] commands [file] # Basic usage
sed '' <file> # Print contents of file; Automatically prints without options
cat <file> | sed '' # Equivalent to above
```

## Printing

```shell
sed 'p' <file> # Prints each line in file _twice_
sed -n 'p' <file> # Suppress automatic printing; Print each line once
sed 20q <file> # Print the first 20 lines of file
```

## Address ranges

```shell
sed -n '1p' <file> # Print first line
sed -n '1,5p' <file> # Print first 5 lines
sed -n '1,+4p' <file> # Equivalent to above
sed -n '1~2p' <file> # Print every other line
```

## Deleting text

```shell
sed '5d' <file> # Delete line 5
sed '1~2d' <file> # Delete every other line starting from the first
sed '6,$d' <file> # Delete from line 6 to end of file
sed -i '1~2d' <file> # Change file in-place
sed -i.bak '1~2d' <file> # Create a backup prior to editing file in-place
```

## Substituting text

```shell
sed 's/<regexp>/<replacement>/g' <file> # Basic usage

sed 's/prev/next/' <file> # Substitute the first instance of `prev` in each line with `next`
sed 's/prev/next/g' <file> # Substitute all instances of `prev` with `next`
sed 's/prev/next/2' <file> # Substitute the second instance of `prev` in each line with `next`
sed -n 's/prev/next/2p' <file> # Print only lines that were substituted
sed 's/PreV/next/i' <file> # Ignore case
sed 's_com/index_org/home_g' <file> # Use _ as delimiter; Replace `com/index` with `org/home`

sed 's/^.*at/(&)/' <file> # Referencing matched text in replacement string
sed 's/$[^ ][^ ]*$ $[^ ][^ ]*$/\2 \1/' <file> # Referencing regex groups; Switch the first two words of each line

sed 's/and/\&/' <file> | sed 's/people/horses/' # Multiple editing sequences
sed -e 's/and/\&/' -e 's/people/horses/' <file> # Equivalent to above
sed 's/and/\&/;s/people/horses/' <file> # Equivalent to above

sed '=' <file> # Insert a line-number on a new line between each existing line
sed 'G' <file> # Insert a blank line between each line

sed '1,3s/.*/Hello/' <file> # Replace the first 3 lines with `Hello`
sed -n '/bash$/p' <file> # Address matching with regex; Print lines ending with `bash`
sed '/^$/d' <file> # Delete blank lines
sed '/^START$/,/^END$/d' <file> # Delete lines between START and END
```

## Hold space and pattern space

```shell
# h/H: Copy/Append pattern space to hold space.
# g/G: Copy/Append hold space to pattern space.
# x: Swap the contents of pattern and hold spaces.

sed -n '1~2h;2~2{H;g;s/\n/ /;p}' <file> # Join adjacent lines
sed -n 'N;s/\n/ /p' <file> # Equivalent to above
```

## Scripting

```shell
sed -f script.sed <file> # Run script.sed on file
```

## Links

- [Chess implemented in sed](https://github.com/bolknote/SedChess)
- [2048 implemented in sed](https://github.com/themattrix/sed2048)
