{"id":235,"date":"2018-07-13T07:42:31","date_gmt":"2018-07-13T07:42:31","guid":{"rendered":"http:\/\/itp7.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=235"},"modified":"2019-05-16T08:24:26","modified_gmt":"2019-05-16T08:24:26","slug":"bash-shell-scripting-3","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/itp7\/chapter\/bash-shell-scripting-3\/","title":{"rendered":"Bash Shell Scripting – 3"},"content":{"raw":"
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  1. Formatting\u00a0output using echo and tput commands in Shell Scripting\u00a0<\/b>echo command<\/strong><\/li>\r\n<\/ol>\r\n \r\n

    In the previous modules, we have used echo in the simplest form. The echo command supports escape sequences to manipulate the output of shell scripts. For instance, we can change the color of text, make it bold or underlined and also insert tab space or newline using echo. Let us go through certain tricks that can be applied while using echo command within shell script. Table 1 lists various options available with echo command and its brief description. While using these options, -e must be used.<\/p>\r\n \r\n

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    The following is an example command followed by its output that uses backspace, tab and newline with echo:<\/p>\r\n$echo -e \"A quick brown\\b\\b\\b fox jumps \\t\\t over the lazy \\n dog\"\r\n\r\n \r\n\r\nOutput:<\/span>\r\n\r\nA quick br fox jumps\u00a0<\/span>dog\u00a0<\/span>over the lazy<\/span>\r\n\r\n<\/div>\r\n

    Special escape sequences can be used with echo command to display text in different colours or to apply formatting to the output text. The following script demonstrates the use of special sequence characters to format the output text. The escape sequences are stored in meaningful variable names. For instance, to make the text underlined, we have used UNDERLINE='\\033[4m'. Here, '\\033[4m' indicates the escape sequence used for underlining the output.<\/p>\r\n \r\n

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    Apart from echo, there is a tput command that can control the way the output is displayed on the screen. The tput command is designed to work for different terminal types of Unix and Linux systems. Few options that are available with tput command are listed in table 2<\/p>\r\n \r\n

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    The following shell script demonstrates the use of tput command with various options. Such options will be helpful when we want to create menu driven scripts that are interactive and which requires the formatting to highlight parts of screen. It is required to use tput sgr0 occasionally to restore the default screen.<\/p>\r\n \r\n

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    1. Debugging Shell scripts and dealing with errors<\/strong><\/li>\r\n<\/ol>\r\n

      At times, while working with scripts and commands, we may face runtime errors. These may be due to errors in the script, such as an incorrect syntax, or missing file or insufficient permission to do an operation. In most of the cases, the errors may be reported with a specific error code or some message, but often just yield incorrect or confusing output. In shell scripting, there are ways and means to identify whether a command has executed successfully or not. The process of identifying errors while executing the shell script is known as debugging.<\/p>\r\n \r\n

      Debugging helps us to troubleshoot and resolve errors, it is one of the most important task that is usually performed by programmers and system administrators.<\/p>\r\n \r\n

      There are two popular ways to debug in shell scripting. They are as follows:<\/p>\r\n\r\n