Home / Questions / 304649
Accepted
moneyBox
Asked: 2020-10-30 14:13:17 +0800 CST 2020-10-30 14:13:17 +0800 CST

How do I compare an argument to a string in Bash? [duplicate]

  • 772

I'm having trouble passing arguments to my script in bash. To simplify I made this example that in the same way does not work.

It is supposed that when invoking it as it programa.sh piedrashould give you a message, if it does not match the expected one it gives you an error. But it doesn't work for me, it always says "PAPER":

#!/bin/bash
# programa.sh

if [ "$1"="papel" ]; then
        echo -e ""
        echo -e "Hola invocaste PAPEL"
        echo -e ""
elif [ "$1"="piedra" ]; then
        echo -e ""
        echo -e "Hola invocaste PIEDRA"
        echo -e ""
else
        echo -e "Error: solo se soportan los argumento: papel y piedra"
fi
bash

1 Answers

  1. Best Answer

    The arguments can go between quotes, in fact this way the is preserved IFSand the separation by these is avoided in case the parameter contains a character belonging to the IFS(tab, space, line break)

    Your main problem lies in the spaces in the evaluator[]

    That is, instead of

    [ "$1"="papel" ]

    It would have to be

    [ "$1" = "papel" ]  # Nota los espacios entre "$1" e = y "papel"

    You can safely use the operator =because it compares strings inside the evaluator [.

    For Bash to understand a token , it checks based on the separators (tab, space, line break), that is, what the variable contains IFS. The operator [would parse based on some token, in this case "=", and to be recognized as such it must be separated from the rest by spaces, otherwise you are just concatenating the argument "$1" to the string "=" and to the string "paper"; that will always evaluate to true, since it's a non-empty string, and will always give you the "Hello, you invoked PAPER" block.

    Once you put the spaces, your code should look something like this.

    #!/bin/bash
# programa.sh

if [ "$1" = "papel" ]; then
#        |_|__ Aqui van los espacios.
        echo -e ""
        echo -e "Hola invocaste PAPEL"
        echo -e ""
elif [ "$1" = "piedra" ]; then
#          |_|__ Aqui van los espacios.
        echo -e ""
        echo -e "Hola invocaste PIEDRA"
        echo -e ""
else
        echo -e "Error: solo se soportan los argumento: papel y piedra"
fi
    • 4