在 bash 脚本中运行带有参数的 python 命令时的变量符号

Question

I have a bash script which is running a bunch of python script all with arguments. In order to have a clean code, I wanted to use variables along the scripts

#!/bin/bash
START=0
SCRIPT_PATH="/opt/scripts/"
IP="192.168.1.111"

if [ "$START" = "0" ]; then
    printf "%s: Starting\n" "$DATE_TIME"

    PORT=1234
    TEST_FILE="$SCRIPT_PATH/Test Scripts/test.TXT"
    SCRIPT="$SCRIPT_PATH/script1.py"
    ARGS="-P $SCRIPT_PATH/script2.py -n 15 -p $PORT -i $IP"

    python "$SCRIPT" ${ARGS} -f "${TEST_FILE}" > ./out.log 2>&1 &

fi

This code is actually working but few things I don't understand :

1. Why, if I add quotes around ${ARGS} , the arguments are not parsed correctly by python ? What would be the best way to write this ?
2. What is the best method to add -f "${TEST_FILE}" to the ARGS variable without python blocking on the whitespace and throwing the error: "$SCRIPT_PATH/Test " not found

Answer 1

When you wrap quotes around an argument list, the argument vector receives a single argument with everything that is wrapped in quotes and so, the argument parser fails to do its job properly and you have your issue.

Regarding your second question, it is not easy to embed the quotes into the array, because the quotes will be parsed before being stored in the array, and then when you perform the array expansion to run the command, they will be missing and fail. I have tried this several times with no success.

An alternative approach would mean that you modify a little your script to use a custom internal field separator (IFS) to manually tell what should be considered an argument and what not:

#!/bin/bash
START=0
SCRIPT_PATH="/opt/scripts/"
IP="192.168.1.111"

if [ "$START" = "0" ]; then
    printf "%s: Starting\n" "$DATE_TIME"

    PORT=1234
    TEST_FILE="$SCRIPT_PATH/Test Scripts/test.TXT"
    SCRIPT="$SCRIPT_PATH/script1.py"
    OLD_IFS=$IFS
    IFS=';'
    ARGS="$SCRIPT;-P;$SCRIPT_PATH/script2.py;-n;15;-p;$PORT;-i;$IP;-f;$TEST_FILE"
    python ${ARGS} > ./out.log 2>&1 &
    IFS=$OLD_IFS
fi

As you can see, I replace the spaces in ARGS with semicolons. This way, TEST_FILE variable contents will be considered as a single argument for bash and will be properly populated in argument vector. I'm also moving the script to the argument vector for simplicity, otherwise, Python will not get the proper script path and fail, due to this modification we did to IFS.

Answer 2

I was thinking something like this (with some cruft edited out to make it a standalone example):

#!/bin/bash
SCRIPT_PATH="/opt/scripts/"
IP="192.168.1.111"

PORT=1234
TEST_FILE="$SCRIPT_PATH/Test Scripts/test.TXT"
SCRIPT="$SCRIPT_PATH/script1.py"
set -a ARGS
ARGS=(-P "$SCRIPT_PATH/script2.py" -n 15 -p "$PORT" -i "$IP")
ARGS+=(-f "${TEST_FILE}")

python3 -c "import sys; print(*enumerate(sys.argv), sep='\n')" "${ARGS[@]}"