Merge pull request #4094 from Naereen/patch-5

[bash/en] Small updates
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Andre Polykanine 2021-01-30 12:36:30 +01:00 committed by GitHub
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@ -27,12 +27,12 @@ for the GNU operating system and as the default shell on most Linux distros.
Nearly all examples below can be a part of a shell script
or executed directly in the shell.
[Read more here.](http://www.gnu.org/software/bash/manual/bashref.html)
[Read more here.](https://www.gnu.org/software/bash/manual/bashref.html)
```bash
#!/usr/bin/env bash
# First line of the script is the shebang which tells the system how to execute
# the script: http://en.wikipedia.org/wiki/Shebang_(Unix)
# the script: https://en.wikipedia.org/wiki/Shebang_(Unix)
# As you already figured, comments start with #. Shebang is also a comment.
# Simple hello world example:
@ -198,7 +198,7 @@ then
fi
# Note that =~ only works within double [[ ]] square brackets,
# which are subtly different from single [ ].
# See http://www.gnu.org/software/bash/manual/bashref.html#Conditional-Constructs for more on this.
# See https://www.gnu.org/software/bash/manual/bashref.html#Conditional-Constructs for more on this.
# Redefine command `ping` as alias to send only 5 packets
alias ping='ping -c 5'
@ -325,6 +325,9 @@ echo "#helloworld" | tee output.out >/dev/null
# WARNING: `rm` commands cannot be undone
rm -v output.out error.err output-and-error.log
rm -r tempDir/ # recursively delete
# You can install the `trash-cli` Python package to have `trash`
# which puts files in the system trash and doesn't delete them directly
# see https://pypi.org/project/trash-cli/ if you want to be careful
# Commands can be substituted within other commands using $( ):
# The following command displays the number of files and directories in the
@ -332,15 +335,15 @@ rm -r tempDir/ # recursively delete
echo "There are $(ls | wc -l) items here."
# The same can be done using backticks `` but they can't be nested -
#the preferred way is to use $( ).
# the preferred way is to use $( ).
echo "There are `ls | wc -l` items here."
# Bash uses a `case` statement that works similarly to switch in Java and C++:
case "$Variable" in
#List patterns for the conditions you want to meet
# List patterns for the conditions you want to meet
0) echo "There is a zero.";;
1) echo "There is a one.";;
*) echo "It is not null.";;
*) echo "It is not null.";; # match everything
esac
# `for` loops iterate for as many arguments given:
@ -377,6 +380,13 @@ do
cat "$Output"
done
# Bash can also accept patterns, like this to `cat`
# all the Markdown files in current directory
for Output in ./*.markdown
do
cat "$Output"
done
# while loop:
while [ true ]
do
@ -431,6 +441,8 @@ cut -d ',' -f 1 file.txt
# replaces every occurrence of 'okay' with 'great' in file.txt
# (regex compatible)
sed -i 's/okay/great/g' file.txt
# be aware that this -i flag means that file.txt will be changed
# -i or --in-place erase the input file (use --in-place=.backup to keep a back-up)
# print to stdout all lines of file.txt which match some regex
# The example prints lines which begin with "foo" and end in "bar"
@ -448,7 +460,7 @@ grep -rI "^foo.*bar$" someDir/ # recursively `grep`, but ignore binary files
grep "^foo.*bar$" file.txt | grep -v "baz"
# if you literally want to search for the string,
# and not the regex, use fgrep (or grep -F)
# and not the regex, use `fgrep` (or `grep -F`)
fgrep "foobar" file.txt
# The `trap` command allows you to execute a command whenever your script
@ -457,6 +469,7 @@ fgrep "foobar" file.txt
trap "rm $TEMP_FILE; exit" SIGHUP SIGINT SIGTERM
# `sudo` is used to perform commands as the superuser
# usually it will ask interactively the password of superuser
NAME1=$(whoami)
NAME2=$(sudo whoami)
echo "Was $NAME1, then became more powerful $NAME2"