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For a stats file "L_Hipp_vertexMNI_rand_tfce_p_tstat1.nii.gz" for example, you can get information based on standard FSL reporting (this page has several examples).
The following two commands are probably the most useful:
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[datauser@localhost temp]$ cluster -i L_Hipp_vertexMNI_rand_tfce_p_tstat1.nii.gz t 2-scalarnamec L_Hipp_vertexMNI_rand_tstat1.nii.gz scalarname="1-p" > cluster_p1.txt
- leave off "> cluster...txt" to display on screen