Java Tools & Commands
This example shows how to apply Java Regex to any native command line output. Though there are built in pattern matching facilities with commands like findstr (window),
find/grep (linux) etc but sometimes they are not powerful enough to apply the desired pattern.
Following class shows how to use our familiar Java regex on command line:
package com.logicbig.example;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;
public class JRegex {
public static void main(String[] args) {
if (args.length == 1) {
applyRegex(args[0], null, getInput());
} else if (args.length == 2) {
applyRegex(args[0], args[1], getInput());
} else if (args.length == 3) {
applyRegex(args[0], args[1], args[2]);
} else {
System.err.println("Wrong usage!");
System.out.println("Valid uses:");
System.out.println(" (1) jregex \"pattern\" \"format\" \"text\"");
System.out.println(" (2) externalCommand | jregex \"pattern\"");
System.out.println(" (3) externalCommand | jregex \"pattern\" \"format\"");
System.out.println(" (4) jregex \"pattern\" < myfile.txt");
System.out.println(" (5) jregex \"pattern\" < myfile.txt");
}
}
private static String getInput() {
String input = "";
try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
String line = null;
while (true) {
if ((line = reader.readLine()) != null) {
input += line + "\n";
} else {
break;
}
}
} catch (Exception e) {
System.err.println(e);
}
return input.trim();
}
private static void applyRegex(String patternString, String groupFormat, String input) {
try {
if (groupFormat == null) {
Pattern.compile(patternString)
.matcher(input)
.results()
.forEach(matchResult -> System.out.println(matchResult.group()));
} else {
Pattern pattern = Pattern.compile(patternString);
Matcher m = pattern.matcher(input);
while (m.find()) {
String formattedOutput = getFormattedOutput(m, input, groupFormat);
System.out.println(formattedOutput);
}
}
} catch (PatternSyntaxException e) {
System.err.println(e);
}
}
private static String getFormattedOutput(final Matcher matcher,
final String inputText,
final String formattedReplacement) {
StringBuilder result = new StringBuilder();
int cursor = 0;
while (cursor < formattedReplacement.length()) {
char nextChar = formattedReplacement.charAt(cursor);
if (nextChar == '\\') {
cursor++;
if (cursor == formattedReplacement.length())
throw new IllegalArgumentException("character to be escaped is missing");
nextChar = formattedReplacement.charAt(cursor);
result.append(nextChar);
cursor++;
} else if (nextChar == '$') {//does not support named groups
// Skip past $
cursor++;
if (cursor == formattedReplacement.length())
throw new IllegalArgumentException(
"Illegal group reference: group index is missing");
nextChar = formattedReplacement.charAt(cursor);
int refNum = -1;
// The first number is always a group
refNum = nextChar - '0';
if ((refNum < 0) || (refNum > 9))
throw new IllegalArgumentException(
"Illegal group reference");
cursor++;
// Capture the largest legal group string
boolean done = false;
while (!done) {
if (cursor >= formattedReplacement.length()) {
break;
}
int nextDigit = formattedReplacement.charAt(cursor) - '0';
if ((nextDigit < 0) || (nextDigit > 9)) { // not a number
break;
}
int newRefNum = (refNum * 10) + nextDigit;
if (matcher.groupCount() < newRefNum) {
done = true;
} else {
refNum = newRefNum;
cursor++;
}
}
// Append group
if (matcher.start(refNum) != -1 && matcher.end(refNum) != -1)
result.append(inputText, matcher.start(refNum), matcher.end(refNum));
} else {
result.append(nextChar);
cursor++;
}
}
return result.toString();
}
}
Compile above class and create a batch file:
jregex.bat@echo off
java.exe -classpath target\classes com.logicbig.example.JRegex %*
If you are using Linux then create following bash script:
jregex.sh#!/bin/bash
java -classpath target/classes com.logicbig.example.JRegex $*
Let's see how to use it.
The normal 'dir' command in windows:
D:\java-command-line-regex>dir
D:\java-command-line-regex>dir
Volume in drive D is Data
Volume Serial Number is 68F9-EDFA
Directory of D:\java-command-line-regex
12/28/2018 11:17 AM .
12/28/2018 11:17 AM ..
12/28/2018 11:17 AM .idea
01/04/2019 10:47 PM 669 java-command-line-regex.iml
12/27/2018 11:06 PM 96 jregex.bat
12/27/2018 10:35 PM 907 pom.xml
12/27/2018 10:35 PM src
12/27/2018 11:04 PM target
3 File(s) 1,672 bytes
5 Dir(s) 20,447,772,672 bytes free
Let's use our program to list only directories:
D:\java-command-line-regex>dir | jregex .*DIR.*
01/05/2019 01:47 AM <DIR> .
01/05/2019 01:47 AM <DIR> ..
12/28/2018 11:17 AM <DIR> .idea
12/27/2018 10:35 PM <DIR> src
12/27/2018 11:04 PM <DIR> target
Let's view only directory names and their modified time in our desired format:
D:\java-command-line-regex>dir | jregex "(\d.*\w\w).*DIR.* [ ]*(.*)" "modified: $1, dir: $2"
modified: 01/05/2019 01:47 AM, dir: .
modified: 01/05/2019 01:47 AM, dir: ..
modified: 12/28/2018 11:17 AM, dir: .idea
modified: 12/27/2018 10:35 PM, dir: src
modified: 12/27/2018 11:04 PM, dir: target
Finding Java Programs in tasklist:
D:\java-command-line-regex>tasklist | jregex .*java.*
java.exe 28808 Console 7 84,192 K
java.exe 26672 Console 7 126,640 K
java.exe 18604 Console 7 2,730,368 K
java.exe 16852 Console 7 318,860 K
java.exe 22052 Console 7 31,772 K
Finding only Java programs in tasklist that have current memory consumption in thousands or more:
D:\java-command-line-regex>tasklist | jregex .*java.*[\d,]{7,}.*
java.exe 26672 Console 7 126,640 K
java.exe 18604 Console 7 2,732,076 K
java.exe 16852 Console 7 318,860 K
Finding <plugins> section of our example project's pom.xml:
D:\java-command-line-regex>jregex "(?s)<plugins>.*</plugins>" < pom.xml
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<source>11</source>
<target>11</target>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
</plugins>
Listing plugins' artifacts in effective pom:
D:\java-command-line-regex>mvn help:effective-pom | jregex "(?s)<plugin>.*?<artifactId>(.*?)</artifactId>.*?</plugin>" $1
maven-antrun-plugin
maven-assembly-plugin
maven-dependency-plugin
maven-release-plugin
maven-compiler-plugin
maven-clean-plugin
maven-resources-plugin
maven-jar-plugin
maven-surefire-plugin
maven-install-plugin
maven-deploy-plugin
maven-site-plugin
To use this utility program anywhere, set the jregex.bat/jregex.sh in the system PATH.
In linux you have to escape $ (as \$) in the format part or use single quotes e.g:
$ ls -la | ./jregex.sh ".*(\d\d:\d\d).*" '$1'
01:47
22:34
11:17
22:47
01:39
01:47
22:35
22:35
23:04
Also check out our Java Regex tutorials to learn to apply more complex regex patterns.
Example ProjectDependencies and Technologies Used:
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