128 lines
3.7 KiB
Markdown
128 lines
3.7 KiB
Markdown
# [The Missing Semester of your CS education](https://missing.csail.mit.edu/)
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## 1. [The shell](https://missing.csail.mit.edu/2020/course-shell/)
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Create new file:
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```bash
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touch hello.txt
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```
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Write to new file / delete everything and write new:
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```bash
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echo 'my_string' > hello.txt
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```
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Append to file
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```bash
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echo 'my_string' >> hello.txt
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```
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To write two commands at the same time, use `|`. Also so that the output of the first command is the input to the second.
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Write multiline string:
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```bash
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echo -e "Hello \nWorld \n" >> greetings.txt
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```
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Given a file with content:
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```bash
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#!/bin/sh
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curl --head --silent https://missing.csail.mit.edu
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```
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Make it executable and execute it
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```bash
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chmod +x my_file
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./my_file
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```
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[Stackoverflow info](https://askubuntu.com/a/229592):
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> Generally, using ./filename.sh specifies a file in the current directory and using filename.sh specifies a file in the current directory or any directory of PATH. The first usage removes any uncertainty as to which file is accessed. In this case, you are attempting to execute the script with bash or another interpreter (by virtue of assumed #!/bin/bash as first line in your script) just by entering the filename. This usage requires the directory is specified. Alternatively, you can try bash filename.sh which seems to work with unspecified directory.
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To find in file:
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```bash
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grep my_string file.txt
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```
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Run script, find string in string and output to file
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```bash
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./semester | grep 'my_string' > last-modified.txt
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```
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Use `grep -o` to display only matched pattern, `grep -P` for regex. [See stackoverflow](https://unix.stackexchange.com/a/13472)
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## 2. [Shell tools and scripting](https://missing.csail.mit.edu/2020/shell-tools/)
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### 2.1. Shell scripting
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Add text to each file in directory, capture many files at the same time:
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```bash
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cp /path/to/project/{foo,bar,baz}.sh /newpath
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mv *{.py,.sh} folder
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```
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### 2.2. Shell tools
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```bash
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# Find all directories named src
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find . -name src -type d
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# Find all python files that have a folder named test in their path
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find . -path '**/test/**/*.py' -type f
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# Find all files modified in the last day
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find . -mtime -1
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# Find all zip files with size in range 500k to 10M
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find . -size +500k -size -10M -name '*.tar.gz'
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# Delete all files with .tmp extension
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find . -name '*.tmp' -exec rm {} \;
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# Find all PNG files and convert them to JPG
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find . -name '*.png' -exec convert {} {.}.jpg \;
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```
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`find` finds files/filenames, to find content inside files use `grep`. Some of the flags include `-C` for getting context lines around it, or `-v` for inverting the result, getting those lines that don't match the pattern. `-R` for recursively iterating in directories.
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Alternatives like `rg` expand the capabilities of `grep -R` by ignoring .git files, etc.
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```bash
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# Find all python files where I used the requests library
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rg -t py 'import requests'
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# Find all files (including hidden files) without a shebang line
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rg -u --files-without-match "^#!"
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# Find all matches of foo and print the following 5 lines
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rg foo -A 5
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# Print statistics of matches (# of matched lines and files )
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rg --stats PATTERN
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```
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> Finding shell commands
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```bash
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# find shell commands where you used apt
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history | grep apt
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```
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Another trick is Ctrl+R, you can insert a subtring to find matching shell commands. By pressing Ctrl+R again, you can iterate through them. Tools for seeing history-based autosuggestions: [zsh](https://github.com/zsh-users/zsh-history-substring-search).
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> Navigating directories
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You can use [fasd](https://github.com/clvv/fasd) to autojump to common directories that you visit often.
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To list all files in a directory in
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* human readable
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* show hidden
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* print details
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* sort by date
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, do `ls -halt`.
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