The underscore variable is set at shell startup and contains the absolute file name of the shell or script being executed as passed in the argument list. Subsequently, it expands to the last argument to the previous command, after expansion. It is also set to the full pathname of each comm...
if [ -z "$var" ]; then echo "var is unset"; else echo "var is set to '$var'"; fi This is because it doesn't distinguish between a variable that is unset and a variable that is set to the empty string. That is to say, ifvar='', then the above solution will incorrectly ou...
if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi 参考:https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash 6、换算秒为分钟、小时 代码语言:javascript 复制 #!/bin/bash a=60100 swap_seconds () { SEC=$1...
Use theechocommand to expand variables. For example, the $PATH shell variable can be expanded by running: $>echo$PATH [ Download now:A sysadmin's guide to Bash scripting. ] Use the find command Thefindcommand is probably one of the most used tools within the Linux operating system. It is...
bash shell参数展开(Shell Parameter Expansion):替换变量(variable)中的字符串 在写bash shell脚本时,如果遇到要替换变量中的字符串,首先想到的就是用sed命令,比如下面的示例将变量str中的数字123替换成UUU: $ str=hello,word,123 $ echo...$str | sed -E -e 's/[0-9]/U/g' hello,word,UUUU 上面的...
tion,declareandtypeset makeeachname local,aswiththe local command, unless the -goptionissup‐ plied.Ifa variable nameisfollowedby=value, the valueofthe variableissettovalue.Whenus‐ ing -aor-Aandthe compound assignment syntaxtocreate array variables, additional attributesdonottakeeffectuntilsubsequent...
- Test if a given variable is [eq]ual/[n]ot [e]qual/[g]reater [t]han/[l]ess [t]han/[g]reater than or [e]qual/[l]ess than or [e]qual to the specified number: [[ $variable -eq|ne|gt|lt|ge|le integer ]] - Test if the specified variable has a [n]on-empty value:...
Why is printf better than echo? How to check if a variable is set in Bash? SettingIFSfor a single statement readarray(akamapfile) issue Tools Match command-line arguments to their help text Bash/Tcsh Comparison Table Collections of scripts ...
<--- Variable is not set [user1@workstation ~]$ The above solution is working on Fedora 11 and RHEL6, but is not working in RHEL5 ? Resolution 'eval' command can be used instead of 'source' with a subshell . 'eval' is really the better choice for this situation including on Fedor...
# Set the value of var to var2 if var2 is greater than var. # var: variable to set. # var2>var: Condition to test. # ?var2: If the test succeeds. # :var: If the test fails. ((var=var2>var?var2:var)) TRAPS 陷阱允许脚本在各种信号上执行代码。在pxltrm(用bash编写的像素艺术...