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MIT-- 讲座课程Shell脚步基础

2020-12-08 08:14:32 osc_43xj61td

Bash 变量和字符串 

 

Bash 中的函数

mcd () {
    mkdir -p "$1"
    cd "$1"
}

 

Here $1 is the first argument to the script/function. Unlike other scripting languages, bash uses a variety of special variables to refer to arguments, error codes, and other relevant variables. Below is a list of some of them. A more comprehensive list can be found here.

  • $0 - Name of the script
  • $1 to $9 - Arguments to the script. $1 is the first argument and so on.
  • $@ - All the arguments
  • $# - Number of arguments
  • $? - Return code of the previous command
  • $$ - Process identification number (PID) for the current script
  • !! - Entire last command, including arguments. A common pattern is to execute a command only for it to fail due to missing permissions; you can quickly re-execute the command with sudo by doing sudo !!
  • $_ - Last argument from the last command. If you are in an interactive shell, you can also quickly get this value by typing Esc followed by .

一个shell脚本程序例子

#!/bin/bash

echo "Starting program at $(date)" # Date will be substituted

echo "Running program $0 with $# arguments with pid $$"

for file in "$@"; do
    grep foobar "$file" > /dev/null 2> /dev/null
    # When pattern is not found, grep has exit status 1
    # We redirect STDOUT and STDERR to a null register since we do not care about them
    if [[ $? -ne 0 ]]; then
        echo "File $file does not have any foobar, adding one"
        echo "# foobar" >> "$file"
    fi
done

下面一些Shell编程技巧

 

convert image.{png,jpg}
# Will expand to
convert image.png image.jpg

cp /path/to/project/{foo,bar,baz}.sh /newpath
# Will expand to
cp /path/to/project/foo.sh /path/to/project/bar.sh /path/to/project/baz.sh /newpath

# Globbing techniques can also be combined
mv *{.py,.sh} folder
# Will move all *.py and *.sh files


mkdir foo bar
# This creates files foo/a, foo/b, ... foo/h, bar/a, bar/b, ... bar/h
touch {foo,bar}/{a..h}
touch foo/x bar/y
# Show differences between files in foo and bar
diff <(ls foo) <(ls bar)
# Outputs
# < x
# ---
# > y

文件查找

Finding files

One of the most common repetitive tasks that every programmer faces is finding files or directories. All UNIX-like systems come packaged with find, a great shell tool to find files. find will recursively search for files matching some criteria. Some examples:

 # Find all directories named src
find . -name src -type d
# Find all python files that have a folder named test in their path
find . -path '*/test/*.py' -type f
# Find all files modified in the last day
find . -mtime -1
# Find all zip files with size in range 500k to 10M
find . -size +500k -size -10M -name '*.tar.gz'

Beyond listing files, find can also perform actions over files that match your query. This property can be incredibly helpful to simplify what could be fairly monotonous tasks.

# Delete all files with .tmp extension
find . -name '*.tmp' -exec rm {} \;
# Find all PNG files and convert them to JPG
find . -name '*.png' -exec convert {} {}.jpg \;

 

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本文为[osc_43xj61td]所创,转载请带上原文链接,感谢
https://my.oschina.net/u/4355739/blog/4780338