对于想了解Bash：if[“echotest”==“test”];然后回声“回声测试输出测试shell”fi;可能？的读者，本文将是一篇不可错过的文章，并且为您提供关于BashShell:CheckF

对于想了解Bash：if [“echo test”==“test”];然后回声“回声测试输出测试shell”fi;可能？的读者，本文将是一篇不可错过的文章，并且为您提供关于Bash Shell: Check File Exists or Not、bash – “export”在shell编程中做什么？、bash – 从shell脚本运行jest测试 – 有失败导致脚本退出、bash – 如何在交互式shell脚本中使“echo”ed行可编辑？的有价值信息。

• Bash：if [“echo test”==“test”];然后回声“回声测试输出测试shell”fi;可能？
• Bash Shell: Check File Exists or Not
• bash – “export”在shell编程中做什么？
• bash – 从shell脚本运行jest测试 – 有失败导致脚本退出
• bash – 如何在交互式shell脚本中使“echo”ed行可编辑？

Bash：if [“echo test”==“test”];然后回声“回声测试输出测试shell”fi;可能？

if [ "echo test" == "test"]; then
  echo "echo test outputs test on shell"
fi

if [ $(echo test) = "test" ] ; then
  echo "Got it"
fi

"`echo test`"

"$(echo test)"

Bash Shell: Check File Exists or Not

How do I test existence of a text file in bash running under Unix like operating systems?

You need to use the test command to check file types and compare values. The same command can be used to see if a file exist of not. The syntax is as follows:

test -e filename
[ -e filename ]
 
test -f filename
[ -f filename ]

The following command will tell if a text file called /etc/hosts exists or not using bash conditional execution :

[ -f /etc/hosts ] && echo "Found" || echo "Not found"

Sample outputs:

Found

The same code can be converted to use with if..else..fi which allows to make choice based on the success or failure of a test command:

#!/bin/bash
file="/etc/hosts"
if [ -f "$file" ]
then
	echo "$file found."
else
	echo "$file not found."
fi

File test operators

The following operators returns true if file exists:

-b FILE
              FILE exists and is block special

       -c FILE
              FILE exists and is character special

       -d FILE
              FILE exists and is a directory

       -e FILE
              FILE exists

       -f FILE
              FILE exists and is a regular file

       -g FILE
              FILE exists and is set-group-ID

       -G FILE
              FILE exists and is owned by the effective group ID

       -h FILE
              FILE exists and is a symbolic link (same as -L)

       -k FILE
              FILE exists and has its sticky bit set

       -L FILE
              FILE exists and is a symbolic link (same as -h)

       -O FILE
              FILE exists and is owned by the effective user ID

       -p FILE
              FILE exists and is a named pipe

       -r FILE
              FILE exists and read permission is granted

       -s FILE
              FILE exists and has a size greater than zero

       -S FILE
              FILE exists and is a socket

       -t FD  file descriptor FD is opened on a terminal

       -u FILE
              FILE exists and its set-user-ID bit is set

       -w FILE
              FILE exists and write permission is granted

       -x FILE
              FILE exists and execute (or search) permission is granted

(Fig.01: File test operators taken from bash man page)

The syntax is same (see File operators (attributes) comparisons for more info):

if [ operator FileName ]
then
     echo "FileName - Found, take some action here"
else
   echo "FileName - Not found, take some action here"
fi

bash – “export”在shell编程中做什么？

$ env | grep '^variable='
$                                 # No environment variable called variable
$ variable=Hello                  # Create local (non-exported) variable with value
$ env | grep '^variable='
$                                 # Still no environment variable called variable
$ export variable                 # Mark variable for export to child processes
$ env | grep '^variable='
variable=Hello
$
$ export other_variable=Goodbye   # create and initialize exported variable
$ env | grep '^other_variable='
other_variable=Goodbye
$

$ othervar=present
$ (echo $othervar; echo $variable; variable=elephant; echo $variable)
present
Goodbye
elephant
$ echo $variable
Goodbye
$

bash – 从shell脚本运行jest测试 – 有失败导致脚本退出

{
  "scripts": {
     "test": "jest","jest": {
    "scriptPreprocessor": "../shared/preprocessor.js"
  }
}

script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
parent_dir="$script_dir/.."

echo
echo "Running all tests..."
find "$parent_dir" -name package.json -maxdepth 2 -execdir npm test \;

FAIL  js/components/__tests__/ExperienceCampaign-tests.js (13.19s)
● ExperienceCampaign › listening to ExperienceCampaignStore › it starts listening when the component is mounted
  - Expected: true toBe: false
        at Spec.<anonymous> (/Users/jonathan/experience-studio/campaign/js/components/__tests__/ExperienceCampaign-tests.js:54:26)
        at Timer.listOnTimeout [as ontimeout] (timers.js:112:15)
1 test Failed,0 tests passed (1 total)
Run time: 13.748s
npm ERR! Test Failed.  See above for more details.
npm ERR! not ok code 0

{
  "scripts": {
     "test": "jest --forceExit","jest": {
    "scriptPreprocessor": "../shared/preprocessor.js"
  }
}

bash – 如何在交互式shell脚本中使“echo”ed行可编辑？

echo "$SUGGESTION\c"
INPUT=`ed -` # problem with this approach is that 'ed' starts in command mode 
             # by default,and I would need input mode

echo "$SUGGESTION\c"
read -e INPUT # doesn't work as advertised

read -e -i "$SUGGESTION" INPUT

#include <stdio.h>
#include <readline/readline.h>

int main(int argc,char **argv)
{
    if (argc != 2)
        return 1;

    // stuff the input buffer with the default value
    char *def = argv[1];
    while (*def) {
        rl_stuff_char(*def);
        def++;
    }

    // let the user edit
    char *input = readline(0);
    if (!input)
        return 1;
    // write out the result to standard error
    fprintf(stderr,"%s",input);
    return 0;
}

myread "$SUGGESTION" 2> some_temp_file
if [ $? -eq 0 ] ; then 
  # some_temp_file contains the edited value
fi

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