Run java -jar forge-1.7.2-10.12.2.1161-mc172-installer.jar 2

C:\Users\r\Downloads>java -jar forge-1.7.2-10.12.2.1161-mc172-installer.jar
Considering library net.minecraftforge:forge:1.7.2-10.12.2.1161-mc172
Considering library net.minecraft:launchwrapper:1.9
Considering library org.ow2.asm:asm-all:4.1
Considering library org.scala-lang:scala-library:2.10.2
Checking "C:\Users\r\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-l
ibrary\2.10.2\scala-library-2.10.2.jar" internal checksums
    checksums.sha1 validated successfully
    Jar contents validated successfully
Considering library org.scala-lang:scala-compiler:2.10.2
Checking "C:\Users\r\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-c
ompiler\2.10.2\scala-compiler-2.10.2.jar" internal checksums
    checksums.sha1 validated successfully
    Jar contents validated successfully
Considering library java3d:vecmath:1.3.1
Considering library net.sf.trove4j:trove4j:3.0.3
Considering library com.ibm.icu:icu4j-core-mojang:51.2
Considering library net.sf.jopt-simple:jopt-simple:4.5
Considering library lzma:lzma:0.0.1
Considering library com.paulscode:codecjorbis:20101023
Considering library com.paulscode:codecwav:20101023
Considering library com.paulscode:libraryjavasound:20101123
Considering library com.paulscode:librarylwjglopenal:20100824
Considering library com.paulscode:soundsystem:20120107
Considering library io.netty:netty-all:4.0.10.Final
Considering library com.google.guava:guava:15.0
Considering library org.apache.commons:commons-lang3:3.1
Considering library commons-io:commons-io:2.4
Considering library net.java.jinput:jinput:2.0.5
Considering library net.java.jutils:jutils:1.0.0
Considering library com.google.code.gson:gson:2.2.4
Considering library com.mojang:authlib:1.3
Considering library org.apache.logging.log4j:log4j-api:2.0-beta9
Considering library org.apache.logging.log4j:log4j-core:2.0-beta9
Considering library org.lwjgl.lwjgl:lwjgl:2.9.0
Considering library org.lwjgl.lwjgl:lwjgl_util:2.9.0
Considering library org.lwjgl.lwjgl:lwjgl-platform:2.9.0
Considering library org.lwjgl.lwjgl:lwjgl:2.9.1-nightly-20131017
Considering library org.lwjgl.lwjgl:lwjgl_util:2.9.1-nightly-20131017
Considering library org.lwjgl.lwjgl:lwjgl-platform:2.9.1-nightly-20131017
Considering library net.java.jinput:jinput-platform:2.0.5