When echoing a variable it is important to surround the variable" in quotes", otherwise echo will expand the variable and attempt to perform globbing with any files that match in the current directory. When you reference a variable in bash it is important not to put spaces around the equals...
Using ~ in $PATH PATH="$PATH:~/bin" Quoted =~ regex [[$foo=~"fo+"]] Opportunities forgrep -q [[-z $(find/tmp|grep mpg)]] Tautology due to spacing [[$foo==0]] Variable brace expansion (Bash) echo{1..$n} Commands eating loop input whileread host;dossh"$host"uptime...
Storing the regular expression in a shell variable is often a useful way to avoid problems with quoting characters that are special to the shell. It is sometimes difficult to specify a regular expression literally without using quotes, or to keep track of the quoting used by regular expressions ...
Why do I need to write"$foo"? What happens without the quotes? $foodoes not mean"take the value of the variablefoo". It means something much more complex: First, take the value of the variable. Field splitting: treat that value as a whitespace-separated list of fields, and build the ...
A variable in single quotes'is treated as a literal string, and not as a variable. Variables in quotation marks"are treated as variables. To get the value held in a variable, you have to provide the dollar sign$. A variable without the dollar sign$only provides the name of the variable...
In this example we declare simple bash variable and print it on the screen ( stdout ) with echo command. #!/bin/bash STRING="HELLO WORLD!!!" echo $STRING 1. 2. 3. Your backup script and variables: #!/bin/bash OF=myhome_directory_$(date +%Y%m%d).tar.gz ...
Double quotes (”“) enable variable expansion and the interpretation of certain special characters, while single quotes (‘‘) maintain the literal value of each character. Q: What can you do with the tab space in printf? The tab space inprintf(\t) can be used to create horizontal spacing...
VARIABLE=2 然后我们通过 $VARIABLE 引用该变量。这里有一点非常重要，也极容易忽视的就是：千万不要在等号两边加空格。虽然加上空格也不会引起语法错误，但很可能造成意想不到的结果。例如 VARIABLE= 2 这个语句，解释器很可能会将一个空字符串赋值给 VARIABLE，然后运行一个名字叫 2 的脚本。一般常用的 Bash ...
regex`trap'exit 42'sigint# Unportable signal speccmd &> file# Unportable redirection operatorreadfoo < /dev/tcp/host/22# Unportable intercepted filesfoo-bar() { ..; }# Undefined/unsupported function name[$UID= 0 ]# Variable undefined in dash/shlocalvar=value# local is undefined in shtim...
VARIABLE=2 然后我们通过 $VARIABLE 引用该变量。这里有一点非常重要,也极容易忽视的就是:千万不要在等号两边加空格。虽然加上空格也不会引起语法错误,但很可能造成意想不到的结果。例如 VARIABLE= 2 这个语句,解释器很可能会将一个空字符串赋值给 VARIABLE,然后运行一个名字叫 2 的脚本。