官术网_书友最值得收藏!

Striping/altering/sorting/deleting/searching strings with Bash only

So far, we have seen inkling of the power of commands available in Linux, and some of these are among the most powerful: sed and grep. However, while we can easily use these commands together, sed by itself or even using another very useful command called awk, we can leverage Bash itself to shave time and reduce external dependencies in a portable way!

So, how can we do this? Let's begin with a few examples using this Bash syntax:

#!/bin/bash
# Index zero of VARIABLE is the char 'M' & is 14 bytes long
VARIABLE="My test string"
# ${VARIABLE:startingPosition:optionalLength}
echo ${VARIABLE:3:4}

In the preceding example, we can see a special way of calling special substring functionality using ${...} , where VARIABLE is a string variable within your script (or even global), and then the following variable is the :. After the :, there is the startingPosition parameter (remember that strings are just arrays of characters and each character can be addressed by index), and there is another optional semicolon and length parameter (optionalLength). 

If we ran this script, the output would be:

$ bash script.sh
test

How is this possible, you may ask? Well, its possible with Bash's equivalent of substr (a function in C and many other programming languages), and this is achieved through the usr of the ${...}syntax. This tells bash to look inside for a variable named VARIABLE and then for two parameters: to start at byte/character 3 (technically 4 because arrays start at element 0 in Bash) and a length of 4 (to print only four characters). The result of the echo is test.

Can we do more with this, such as removing the last character? Deleting words? Searching? Of course, and all of this is covered in this recipe!

主站蜘蛛池模板: 乌拉特前旗| 东港市| 平原县| 望城县| 武隆县| 疏附县| 阳山县| 浏阳市| 修水县| 马鞍山市| 松江区| 宝兴县| 滨州市| 扶绥县| 长岭县| 罗平县| 龙口市| 高平市| 蒙自县| 新田县| 加查县| 福安市| 榕江县| 孟津县| 专栏| 寿光市| 石泉县| 扎兰屯市| 贵州省| 玛曲县| 平顺县| 屯留县| 莫力| 板桥市| 秦皇岛市| 隆回县| 延庆县| 海伦市| 富锦市| 湘乡市| 淄博市|