How to check if a directory exists? How to check if a command succeeds or failed? How to do string comparison and check if a string equals to a value? How to check if a string is in an array? How to use the Bash ternary operator? How to negate an if condition in a Bash if sta...
Similarly for example we can use while loop to check if file does not exists. This script will sleep until file does exists. Note bash negator "!" which negates the -e option. #!/bin/bash while [ ! -e myfile ]; do # Sleep until file does exists/is created sleep 1 done 1. 2....
"\e.": insert-last-argument 是插入前一个命令行的最后一个参数,在这个功能的附近,还有其它的一组数字命令可以使用,它们用来干什么的呢? "\e-":digit-argument"\e0":digit-argument"\e1":digit-argument"\e2":digit-argument"\e3":digit-argument"\e4":digit-argument"\e5":digit-argument"\e6":digit-...
$ checkarg /home/chris/bin/checkarg: line 10: 1: An argument is required $ checkarg x /home/chris/bin/checkarg: line 10: 2: Two arguments are required $ checkarg '' '' /home/chris/bin/checkarg: line 13: 1: A non-empty argument is required $ checkarg x '' /home/chris/bin/...
if [[ $1 -eq 4 ]] then echo "You entered $1" fi echo "End program" First this program will print “Start program”, then the IF statement will check if the conditional expression[[ $1 -eq 4 ]]is true. It will only be true if you provide4as the first argument to the script...
# The shift command removes one argument from the list of # command line arguments. shift shift # $* contains now all the files: for file in $*; do if [ -f "$file" ] ; then newfile=`echo "$file" | sed "s/${OLD}/${NEW}/g"` ...
Declare a local variable 'num' to store the argument passed to the function. Declare another local variable 'result' and initialize it to 1. Check if 'num' is negative. If it is, we print an error message and exit the script.
Checking if a variable exists ([[ -v varname ]]): Yes, this is possibly a killer argument, but consider the programming style of always setting variables, so you don't need to check if they exist.Are empty string comparisons any special?Of...
Check if there is exactly one argument provided (the username). If not, print usage information and exit with code 1. Next assign the provided username to the variable 'username'. Finally, call the "check_user_existence()" function with the provided username. ...
ifquery: New ifup alias completion (932d0be) _count_args: Add support for not counting specified option args (daf010a) ifup etc: Add option and option argument completion (f499aa3) ssh, scp, sftp: Support completing arg of last bundled short option (645d901) completions/Makefile.am: Use...