Shell Programming Notes

1 Basics

1.1 Pre knowledge

# chmod +rx scriptnameecho"Here"# A whitespace before '#' in commentecho -n $var# echo variable without newline character
hello="A B C D"echo$hello# A B C D (variable reference)echo"$hello"# A B C D (variable itself)if [ -n"${10}" ] # Parameters > $9 must be enclosed in {brackets}.
arch=$(uname -m)# get current OS's archif [ !-f"$filename" ] # Quoting $filename allows for possible spaces.
find ~/ -name 'core*' -exec rm {} \;# Removes all core dump files from user's home directory.

Ctrl-H Erases characters back
Bash sets the “integer value” of a string to 0.
$# : number of parameters
$*/$@ : all the positional parameters. P778
P53 : get keyboard input

1.2 Redirect

1>filename
# Redirect stdout to file "filename."1>>filename
# Redirect and append stdout to file "filename."2>filename
# Redirect stderr to file "filename."2>>filename
# Redirect and append stderr to file "filename."&>filename
# Redirect both stdout and stderr to file "filename."# This operator is now functional, as of Bash 4, final release.
M>N
# "M" is a file descriptor, which defaults to 1, if not explicitly set.# "N" is a filename.# File descriptor "M" is redirect to file "N."
M>&N
# "M" is a file descriptor, which defaults to 1, if not set.# "N" is another file descriptor.# 2>&1 ==> Redirects stderr to stdout. >&j
# Redirects, by default, file descriptor 1 (stdout) to j. # All stdout gets sent to file pointed to by j.

2 Useful Tips

space do matters
Sed almost always runs faster than awk
tree ignore by pattern link $tree -I ‘node_module*’ to ignore node_modules/

mess stuff

cat {file1,file2,file3} > combined_file
# Concatenates the files file1, file2, and file3 into combined_file.
cp file22.{txt,backup}
# Copies "file22.txt" to "file22.backup"
(cd /source/directory && tar cf - . ) | (cd /dest/directory && tar xpvf -)
# Move entire file tree from one directory to another # abs-guide P28echo`date`| pbcopy
# get date string into clipboard read -p "Want to start? (y/n) " res
if [ "$res"="y"];then# do blah blahelse# do blah blahfi

3 Archieve

3.1 Create

$tar -cvf filename.tar ./path/file (dir) <–不压缩 $tar -zcvf filename.tar.gz ./path/file (dir) <–以 gzip 压缩 $tar -jcvf filename.tar.bz2 ./path/file (dir) <–以 bzip2压缩

3.2 Unzip

$tar -xvf filename.tar $tar -zxvf filename.tar.gz <–注意后缀要对应写正确 $tar -jxvf filename.tar.bz2

3.3 tee

pipe standard output to terminal and new file at same time ls | tee new_file

3.4What does ‘source’ do?

executes the content of the file passed as argument

3.5 圖片白色轉透明

mogrify -transparent white image*.png

3.6 Execute founded files

find . -name “*.pyc” –exec rm -rf {} \; # delete files recursively
find . -name “.DS_Store” -print0 | xargs -0 rm -rf # delete directories recursively # print0 ensure file name contains space interpreted corretly
find . -depth 1 -name ”.py” –exec cp ‘{}’ ./destination \; *in OSX, is -exec [only one dash]

3.7 execute find results

3.8 colorful less

less file, then press v

FilesExpand file tree

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