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copied!<p>I'd probably go for John's <code>sed</code> solution but, since you asked about <code>awk</code> as well:</p> <pre><code>$ echo 'Line1: I just want to make clear of the problem Line2: Thanks to all who look into my problem Line3: How to solve the problem? Line4: Thanks to all.' | awk '/^Line2:/{$0=$0" Please help me"}{print}' </code></pre> <p>This outputs:</p> <pre><code>Line1: I just want to make clear of the problem Line2: Thanks to all who look into my problem Please help me Line3: How to solve the problem? Line4: Thanks to all. </code></pre> <p>An explanation as to how it works may be helpful. Think of the <code>awk</code> script as follows with conditions on the left and commands on the right:</p> <pre><code>/^Line2:/ {$0=$0" Please help me"} {print} </code></pre> <p>These two <code>awk</code> clauses are executed for every single line processed.</p> <p>If the line matches the regular expression <code>^Line2:</code> (meaning "Line2:" at the start of the line), you change <code>$0</code> by appending your desired string (<code>$0</code> is the entire line as read into <code>awk</code>).</p> <p>If the line matches the empty condition (all lines will match this), <code>print</code> is executed. This outputs the current line <code>$0</code>.</p> <p>So you can see it's just a simple program which modifies the line where necessary and outputs the line, modified or not.</p> <hr> <p>In addition, you may want to use <code>/^Line2:/</code> as the key even for a <code>sed</code> solution so you don't pick up <code>Line2</code> in the middle of the text or <code>Line20</code> through <code>Line29</code>, <code>Line200</code> through <code>Line299</code> and so on:</p> <pre><code>sed '/^Line2:/s/$/ Please help me/' </code></pre>

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